if you don’t have the user name, then there is not a problem at all , you can get your user id so easily, but if you are having some user name and you want to work with your user id, then you can have that by the following steps.
STEP 1: Open your facebook account.
STEP 2:Click on your Facebook profile picture.
STEP 3: Then you will be redirected to your timeline page or your personal page and that will look like as follows, and the in the address bar the link will change to the “https://www.facebook.com/YOUR-USERNAME or someone’s USERNAME ”
and after changing that, hit the enter key and you will see some kind of your information shown above, thus how you can get your user id as well as your friend’s user id.
i hope this post may help you to get your user id anytime.