The deadline for registering to vote is 18th June 11:59pm (that's tomorrow!). It only takes 5 minutes to register online.
You can register online here: Register to vote
The deadline for the postal vote is at 5pm 19th June (Wednesday) if you would like to vote via postal vote, if you think you cannot get to your local polling station that day.
You can apply for your postal vote here: Apply for a postal vote