Ok, this is the first time I'm thinking about filing a patent, and I don't know where to start. First of all I'm not from the USA but I want to file a patent with the USPTO without a patent attorney as I can't afford one. Can be a patent filed onlne? Where can I get detailed information about the procedures and fees? And most important, if there is a similar patent, can I be sued from the owner? Thanks!
Be careful, in the interest of protecting national security, your first patent filing might need to be in a patent office within your country of residence or where the invention was made (conceived).
For example, a patent application for an invention made in (conceived within) the US must first be filed with the USPTO (or must otherwise have authorization to be filed abroad). See 35 USC 184 ==> http://www.uspto.gov/web/offices/pac/mpep/s140.html and 35 USC 181 ==> http://www.uspto.gov/web/offices/pac/mpep/mpep-9015-appx-l.html#d0e304551
Filing a patent with USPTO is an easy part, and you can definitely do it yourself. It costs around $800 to file as a Small Entity.
Current USPTO fees can be found here: http://www.uspto.gov/web/offices/ac/qs/ope/fee010114.htm
However, you'd most likely need an attorney to draft a patent application and respond to Office Actions during patent prosecution (when your claims get rejected, etc.) That's where it gets really expensive. I cut costs by finding a patent attorney on sites like Elance.