1. Sign in to your Twitter account and locate the account you wanna block.
2. Now click on person icon displayed on the user profile.
3. Select Block @username from drop down menu.
4. Now that user account won't be able to interact with you anymore until you unblock that user.
* In case if you change your mind or mistakenly blocked a wrong user account, you can unblock that user in a single click.
How to Unblock a Twitter User Account
i. Locate the blocked user account.
ii. Now either click Blocked button or click person icon and select Block @username from drop down menu.