Any photographer worth their weight will know how to do this for you, however, it's good for you to know too so that you're prepared on the day. To be honest though in the rush of the getting ready and the joy of that first kiss, you may forget to think about this, but I'm sure at the time it will come back to you. So the confetti shot you will see in any photographers portfolio is normally posed. Mostly because, and this is generally speaking, to get it to look great and natural, there is an element of not leaving it to chance!
Firstly it's going to depend on the weather and the type of confetti you're using. Anything lighter than rice on a windy day won't go where you need it to for the perfect picture, so your photographer should position you downwind or close as so that when people throw it over you it blows across the frame.
Secondly, it's going to depend on the venue. Not all venues want loads of confetti at their front door so they may move you somewhere else. Now I know it feels awkward to finish the ceremony, have that first kiss, sign the register, then have to walk somewhere else for the confetti. But trust me, it's worth it. For my wedding it's what we had to do to fit in all the guests, and it worked beautifully for the photos.
Lastly, a tunnel or row is what you need to be thinking. Where will the photographer be most likely to stand and do your guests need to form two lines on either side for you to walk through, or stand all on one side so you walk along them as they throw it? Get some ideas from Pinterest of the type of confetti shot you'd like, then show your photographer. Chat to your venue too as they may already have ideas to share from previous weddings, and what they do and don't allow.
Bonus tip... give everyone a small handful, but give the biggest handfull to the guests closest to where the photographer will do their pic...this ensures a shot full of 'fetti! :)