If I have a few things in my cart on ebay and I proceed to checkout will they arrive all together or will they arrive all separate? ?

The final page of the order will tell you where each item will be dispatched from, and on approximately what date. Read it carefully: it's your last chance to change your mind.

They may or may not be altogether.

If they're all from separate sellers, they'll be sent separately. 

If they are from the same seller then they will probably come together.  If they are from different sellers then they will almost certainly come at separate times.

if theyre from the same vendor they will likely all ship and arrive together .. if not then no ...all the cart does on ebay is make it more simple to check out instead of searching and buying things individually ..

You can request that they all be held until the order is complete and sent at the same time. Otherwise, they may be divided into different mailings.

Depends on whether or not you're buying all of the items from the same seller.