No spoilers I think, but I'm working on how to combine items for an early puzzle.

I read on the steps to do it in walkthrough, but can't make it work in game. 

Click on first item, then click and hold on second item, then drag to first item?  I can't get these things to go together? Anyone know what I'm doing wrong?

There's not an awful lot of combining required, but you need to do a few such things. You click on one of the items, such as Rooter's head, to make it show up larger on the left of the other inventory items. Then you drag the item you want to combine with that, such as a bolt, to that large representation. If you've done it right, it will show the combined item in the large view, and will also have a "separate" button so that you can undo it if you made a mistake.

Thank you!!! I kept trying to combine the item with the small icon of rooter's head next to it, not with the large representation on the left.  That solved it, thanks again!!  

I think many people complained about how the inventory combining works during the beta, but sadly, nothing was done to improve it. It's really unintuitive system.

I conquered the same issue and it took me a while to sort this out. Now that I know how it works, it works without flaws. But I share your opinion. Its not very intuitive (like so many things in this game).