How do I create like a rank nametag? Like at the bottom of your name it shows the rank?

This is not a request website. We are a website for requesting help with scripts you have already made. Keep this in mind for future questions.

However, some good things you can look at to achieve your solution is to look at player:GetRankInGroup(), player:GetRoleInGroup() and player:IsInGroup().

An example of this would be:

local player = game.Players.LocalPlayer
local groupID = 2

-- Simple usage of GetRankInGroup()
-- This is used for checking if a user has a certain role ID.
-- 255 is the owner ID.
-- 0 is a guest. (Not in the group)
if player:GetRankInGroup(groupID) == 255 then
    print(player.Name.." is the owner of the group.")
end

-- Simple usage of GetRoleInGroup()
print("Player is ranked as "..player:GetRoleInGroup(groupID))

-- Simple usage of IsInGroup()
if player:IsInGroup(groupID) then
    print("Player is in the group: "..groupID)
else
    print("Player is not in the group: "..groupID)
end

To achieve displaying name ranks, you will have to investigate Billboard Guis.

Hope this helped!