Holding a ukulele while standing up can be a bit tricky - particularly if you're playing something intricate. So many people decide to use a ukulele strap. Unfortunately, most ukuleles are built with traditional over-the-shoulder type straps in mind. So if you want one of those you'll have to install strap buttons on your uke.
A less drastic option is to buy a 'ukulele thong'. These go under the ukulele and latch on to the soundhole. They're sturdy and do the job well. And, also, it gives you the excuse to say 'thong' a lot.