Can I manualy add modules in Drupal 7 just by pasting them in the modules folder?
If you have a single site setup:

Contrib modules go in /sites/all/modules/contrib/

Custom modules go in /sites/all/modules/custom/

Custom themes go in /sites/all/themes/

If you have a multi site setup:

contrib modules go in /sites/site_name/modules/contrib/

custom modules go in /sites/site_name/modules/custom/

custom themes go in /sites/site_name/themes/

I think some of the language in this post is dangerous, remember, do NOT put modules in the root modules directory, that is DRUPAL CORE.  Everything you code and download should go in the directories I've mentioned above.