Gmail will ignore any dot in your email address before @ sign.

According to  Gmail’s support page:
Gmail doesn’t recognize dots as characters within usernames, you can add or remove the dots from a Gmail address without changing the actual destination address; they’ll all go to your inbox, and only yours.

For example: assuming your email address is johndoe@gmail.com, all email directed to john.doe@gmail.com, j.ohn.doe@gmail.com and any other dot-variant addresses will be delivered to your Gmail inbox.

Also, whatever word you put after your <username> and ‘+’ sign and before @ sign, will be ignored.

According to Gmail’s support page:
Gmail doesn’t offer traditional aliases, but you can receive messages sent to your.username+any.alias@gmail.com.

For example: using your my.email@gmail.com, emails sent to these email address will be directed to your inbox: my.email+food@gmail.com, my.email+spam@gmail.com, my.email+evernote@gmail.com and more. Combine this with the ‘dot’ trick to produce a an infinite number of email aliases.

Note that many website / form will block you from using ‘+’ sign in your email address.

Combining both tricks, you can get a simple anti-spam mechanism or customized productivity tool or pretty much infinite email addresses (‘If email is sent to m.y.e.m.a.i.l@gmail.com, direct it to spam folder‘) or a highly customized priority system (‘if email is sent to  my.email+urgent@gmail.com, label and star it‘).