Can someone give me a brief explanation on how to make a leader board(leveling up)?

To make a leaderboard, you have to create a value inside of a Player named 'leaderstats'. Then, create different values inside of the leaderstats value, and they will appear on the leaderboard. Do this with the PlayerAdded event.

game.Players.PlayerAdded:connect(function(plr) --When a player joins
    local stats = Instance.new("IntValue",plr) --Create the value
    stats.Name = "leaderstats" --Name it leaderstats

    local points = Instance.new("IntValue",stats) --Create a value in leaderstats
    points.Name = "Points" --Name it points
    points.Value = 0 --Make the value equal 0
end) --end