Tabs or Tablature for the guitar is a convenient way to learn anything on the guitar removing the need for reading musical notation for example. There are countless Tabs available out there for almost any song. If the song is moderately famous someone has written it down in TAB format. There are of course a lot of problems with quality in many tabs out there but don’t worry the big tab collections have rating systems that let you know how accurate the Tabs are that users submit.
Few years ago you would use programs like PowerTab and GuitarPro to play tabs like midi files but now they seem less important since the big Tablature sites provide web apps that do the same. If you want to write Tabs down in a playable midi format then I recommend checking out the above mentioned programs. They are still the best choice for creating playable midi TABs
Here are some pages worth checking out.
Learn how to read TABS by watching the video