How do I use the builds on this site?

So all these builds say use this item and this item,but my question is what do i use until I get these items.

It depends. Sometimes just use whatever you can find/afford/use that best suits the build, sometimes the item is required for the build to work as intended and you have to do something else that your passive tree is suitable for in the meantime. Both cases are obviously very context-dependent. Which build(s) in particular are you looking at?

Ignore the builds until you can either farm the item or buy it.

Look instead for budget builds that don't require unique, get it to a decent level then start farming.