First you have to have a host and many of us use Pbase or Smugmug. You could also establish your own website if you are savvy enough to do that. Once you have that done you upload your images to the host and subsequently to this forum or others.
Navigate to Pbase and look around. It doesn't cost very much to have a gallery at Pbase and their instructions on doing so are pretty clear. You might want to take a look at my Pbase account to give you an idea. The URL is contained in my signature block.
I just started uploading photos to flickr.com. It's free, and I've been happy with it. As for posting them here, I just type in
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One of many great things about posting here is that your pix can be up to 960 pixels wide, which makes them nice and big and easy for people to see and comment on. So, if you resize before you upload to flickr or wherever (I always decrease mine to 72ppi and 960 pixels wide), make sure not to make them too small.