So, if you own 'gmail.guide [at] gmail.com,' you also own 'gmailguide' and 'g.m.a.i.l.g.u.i.d.e' and 'gm.ai.lg.ui.de,' and many more possibilities!
For security purposes, you can only log in with the exact username you used to create your account. So, if you started with dots, you have to log in with dots, but people who send you messages don't have to include dots.
Also, if you find that you're always receiving spam messages at a variation of your username. For instance, my username is 'gmail.guide' but I always get spam sent to 'gmailguide' and it ends up in my inbox. If that's the case, you can create a filter for messages address to 'gmailguide' and send them directly to Trash.