Typing the title should work, but if it doesn't, there are two easier ways of adding art to a collection.

• Go to the art page, select your collection from the dropdown on the left, and click the add to collection button, or
• On the search results page, select your collection from the "collect into" pulldown on the lower left, then press the plus buttons that appear on the search results.

As I said, typing the title should work.  If you provide me with the collection and asset(s) you're trying to add to it, it might help me debug it or at least figure out what the issue is.

Also, just a random note:

With no instructions what to put in the asset list, what do you guys expect will happen?

I'm just one guy and I write code for this site in my spare time.  I assure you that it wasn't out of laziness or malice that I didn't write instructions.  Time allowing, I'd like to attempt to debug the issue, so it would be really helpful if you could provide me the collection and asset(s) you were having issues with, so I can test.