What is data store, how can i use it and when can i use it?

Datastore is the ability to save data for when you rejoin, leaving a game and rejoining... where did you read about datastore 1 and 2, theres a single datastore with infinite string storages...

Use it if you want to save a players data, heres an example

local ds = game:GetService("DataStoreService"):GetDataStore("Datastore_1")
local CurrentData = 0 -- this will be overwritten in the future...
game.Players.PlayerAdded:Connect(function(p)
    pcall(function()
        local PersonsData = ds:GetAsync(p.UserId)
        local CurrentNewData = PersonsData[1]
    end)
end)
game.Players.PlayerRemoving:Connect(function(p)
    pcall(function()
        local PersonsData = ds:SetAsync(p.UserId,CurrentData)
    end)
end)
while true do wait(1)
    print(CurrentData)
    CurrentData = CurrentData + 1
end

The Datastore_1 is what I believe you think is datastore_1, a string value where everything is basically stored in...

Use the players user id to save stuff...

API services must be on... Basically just saving a value

To save multiple values use a table not multiple of the "GetDataStore"....

Datastores are used for saving any kind of data such as Leaderstats, tools, player location etc.

This may be of some use https://developer.roblox.com/en-us/articles/Data-store