To get 3 months of Discord Nitro you need to add a payment method, after that do not forget to disable auto payment.
You must not have an active Nitro subscription to activate Discord Nitro
The activation process takes 5 to 10 minutes.There may be a delay if there are a lot of orders. If it´s night, you have to wait.
A Discord Nitro subscription gives users access to the following features:
Installing an animated GIF avatar.
Ability to use animated emoji.
Ability to use custom emojis everywhere (if the user has the right to use external emoji on the server).
Maximum upload size changed from 8MB to 100MB or 50MB with Nitro Classic.
Ability to share the screen at 720p 60fps or 1080p 30fps.
Discord Nitro badge in profile.
Ability to change your discriminator. (Note: if your Nitro subscription expires, your discriminator will be randomly selected).
Server boost to give your favorite server exclusive bonuses and a cool badge.
Dedicated profile badge to show everyone that you support Discord.