They are several ways of gathering knowledge today .This is true because no one claim whatever he/she knows all came from him/her, your must have borrowed some part of what you know from some where.
Whatever your are supposed toknow when borrowing knowledge is if that source is reliable or not because you cannot treat all same way, some times people might give you their opinion about some and might be not the truth .
There several sources where human beings get knowledge from, some of those source are written here below.
1. Learning from other people
5.Introspection and lastly
Basically those are some source of knowledge, what are other sources you may know of .