It means joining or making a group, then working with that group to advance common goals. A lot of the specifics depend on your opinions (which political party, if any, to join, whether adventurism is okay, etc.), but unionization for example is generally a kind of organizing that most people support.

Striking and fighting are just a very small part of that, a lot if it is about getting other people to join your group, or somehow convincing people that you are in the right (or, bleh, electoralism (hecking DSA)).