Are you connected to the web? Haha, seriously however, are you?
Presuming you have the appropriate login e-mail and also password (and you're attached to the web) there's a couple of points that could be causing your problems:
How Come I Can't Log Into Facebook
Are you getting a mistake message? If so, check the Facebook help page for explanations and also fixes to known issues.
Ensure you do not have any kind of extensions or antivirus programs running that are obstructing Facebook.
Have you tried getting rid of the app's cache? Go to Settings > Apps > Facebook > Clear Cache. If this doesn't work you can try clearing data as well and as a last hope uninstalling and re-installing the app totally.
Did you join your phone number? Ensure you type in the country code as well when visiting.
If the application is informing you to upgrade your email address, this is probably because your email web server is labeling your Facebook e-mails as spam.
If you've recently enrolled in Facebook you may need to verify your account initially. If you've just recently transformed your password, see to it you're attempting to visit with the brand-new password as well as not the old one.
If you're logging in using a web browser, see to it you have cookies allowed which facebook.com is included in your list of safe sites.
Make certain you have one of the most current variation of the Facebook app for Android.