You'll be able to use all of Discord's chat features, but you must first claim your account by validating your email address. This way, you'll remember your username and Discriminator (the four digits next to your user name), as well as all the servers you've joined.
Simply check the email address you used to establish your account to claim it. Simply tap the Resend button in the orange banner at the top of the app if you don't see an email.
And here will be a message
“Please check your email and follow the instructions to verify your account ”
You're good to go if you click Verify Email in the given email.
Note: Some servers include a security verification wall that prevents you from using the chat functionality unless you have a verified account. More information on server verification levels may be found here.