Pokestops
Pokestops are blue towers with a prism on top. Whenever you approach one and it gets into your radius, it will transform into a tower with a flat circle. To collect items from the pokestop you need to click on it then it will zoom in onto your full screen. After this happens, swipe the screen in order to spin the flat disc. Items that you receive will jump out of the spinning disc and appear to you. To collect the given items you don't need to click on them but just close the pokestop by the x on the bottom of the screen. A cool feature has been noticed about pokestops that when you collect 10 Pokestops in a fairly short amount of time, the tenth pokestop should give more items than the usual amount of three of four.
Pokeballs
Pokeballs are round balls that are used to capture a Pokémon. For example: When a Pokémon appears near you on the map, you need to click on the Pokémon. There will be a quick animation and the game will say for example: "A Pikachu appeared" After this animation, a pokeball will appear at the bottom of the screen. In order to throw the pokeball at the Pokémon to catch it, tap the pokeball and swipe at the Pokémon. The Pokeball will be sent flying. But in a player's case, who is over level 12, the player will be able to click on the button on the bottom right, and you can click on a Great or Ultraball to use it. The pokeball is the simplest pokeball there is in Pokémon Go and it has the least capture rate. The Greatball has a higher capture rate and the Ultraball has the highest capture rate out of all the pokeballs in Pokémon Go. It is still unknown if Niantic will make a Masterball which should have a 100% capture rate, later on in a future update. The Masterball will probably be released in an update where Legendary Pokémon appear, so Pokémon trainers can guarantee themselves a rare catch.
Potions
Potions are used to heal Pokémon like Aerodactyl, Dragonite, Raichu and your other battling Pokémon after gym battles or PvP battles that are yet to come. There are four different potions that are in Pokémon Go. There is the normal Potion, Super Potion, Hyper Potion, and Max Potion. Potion heals 20 HP, Super Potion heals 50 HP, Hyper Potion heals 200 HP and Max Potion heals fully the injured Pokémon. Potions first appear at level 5 along with Gym Battles.
Revives
Revives are items that revive a Pokémon after it has lost all its HP. There are only two types of Revives, normal Revive and Max Revive. Each revive not only revives the Knocked out Pokémon, But also heals it. Normal Revive heals a Pokémon to half of its max HP, while Max Revive fully heals the Pokémon.
Razz Berry
The Razz Berry is a very useful item that is used to increase capture rate to easier catch a Pokémon. To use a Razz Berry while catching a Pokémon, you do just like switching to a different pokeball: press the button on the bottom right, press on the Razz Berry, and when it appears on screen, you can either click on it to use it, or press on the x to cancel and not use it. The Razz berry is most efficient to use on Pokémon that you really want to catch, rare Pokémon, or Pokémon with high CP that you don't want to risk running away.
Stardust and Candy
Stardust and Pokémon Candy are the two necessary things that you need in order to make your Pokémon stronger by either evolving or powering up your Pokémon. Stardust is collected as you catch Pokémon, and as you hatch eggs. Each Pokémon capture gives you 500 Stardust but each egg hatch brings different amounts. You receive 3 Pokémon candies for every catch, each candy corresponding to the Pokémon (Pikachu candy). Another way to get Pokémon candies is by hatching eggs, and an egg can give you a lot of candies all the way up to 20, but the max number is unknown. A power up requires from 1 to 4 candies depending on the Pokémon's hidden level and an amount of stardust from 200 to 10000. An evolution on the other hand, doesn't require any stardust but more candies (12, 25, 50, 100, and 400). An evolution doesn't just raise the cp and HP but gives the Pokémon new moves and a new form or shape, like Pikachu evolves into a Raichu.
Lucky Egg
The lucky egg is the one item that helps get more XP. Although it lasts only 30 minutes, it multiplies the XP you earn by two. The most effective way to use it is to mass evolve your Pokémon while it's active. This way you gain a thousand XP from every Pokémon evolution. Although it's not very effective to use it at places where there are three or four lures, if you have a lot of them it surely helps but not as much.
Incense
The incense is an item that specifically attracts Pokémon to your location and doesn't benefit anyone but yourself. These incenses are best to use when going for a walk where there aren't any lure Modules to do that for you. Another way for using the Incense effectively is by using it when beside lures, because then you'll have twice more Pokémon because they work independently.
Lure Module
The Lure Module is an item that attracts Pokémon to a chosen pokestop. It lasts 30 minutes just like the lucky egg and the Incense. Unlike the Incense which benefits only you, the Lure module benefits all the Pokémon trainers who are around. So if you're going to hunt some Pokémon with a bunch of friends you can find a location where your diameter can reach three or four pokestops and place lures on all of them. This way you don't need to use four lure modules but one or none because only four of you and your friends have to place the Lure Modules on a pokestop. As they do in Pokémon episodes, trainers like Ash Ketchum and most others travel with their friends. Niantic has put that to mind and found that by having group areas where people can come, people can hang out with their friends in one place.
Pokémon Eggs
Pokémon eggs are eggs from which you can hatch Pokémon. There are three different eggs that are currently in Pokémon Go. There is the 2 Km egg, 5 Km egg and a 10 Km egg. The Km that an egg is is the distance that you have to walk, jog, run or cycle in order to hatch it. But there is no cheating on hatching eggs because the game tracks your speed and doesn't count the distance if you're going too fast. To see which Pokémon hatch from each type of egg, see the egg hatching chart: https://rankedboost.com/pokemon-go/egg-hatching-chart/
Egg Incubator
An Egg Incubator is necessary to hatch Pokémon eggs.