At many university in the US, instructors don't teach enough or often they don't even teach at all.
It's all your responsibility to read the textbook and understand.
However, if you don't practice some questions, we don't know if we really understand the material/textbook or not.
Many instructors assign homework but they don't explain the answers well at all.
So, having solutions manuals is critical if you got a bad and lazy instructors ...
Well, test bank is also very useful tool to verify how much we understand the material.
Actually, many teachers often use those test bank for mid-terms or finals, you can understand the material and you can get a good grade ;)
Here are some study guide links
Click below items if you are interested
Solutions Manual