Just to add a little more to your potential confusion, Sandy.
If you do consider having a separate photo hosting site there are so many to choose from!
After initially testing several, and failing to even get into some, I went for P base which does make a small charge; but for that payment you get an easy to use safe and secure system with a fair bit of flexibility. No adverts popping up everywhere or any worries about being hacked etc.
One advantage of this method is that you can create specific galleries of images which are easily viewed by your chosen friends or the whole world, depending on your settings. For example all my chosen images are at
www.pbase.com/crustacean
And they are available to be viewed worldwide not just on specific postings in specialist sites like CinC.
Regarding image sizes for uploading. Straight from camera is too large for internet use so any site which accepts this sort of upload will automatically resize the images; and their method may cause some softness compared to doing it yourself with 'proper photo editing software'. I sometimes add a little bit of extra sharpening after substantial resizing - but that is a topic for another day.
As Dave mentioned, average screen size gives the best and easiest to upload results. For example, start by setting the resolution to 96 pixels per inch (European) or 72 ppi (USA) monitor resolution. In reality, either will work fine.
Then set the image size, using the pixel option, to somewhere between 1000 and 1500 pixels (average usable sizes) on the width OR about 1000 pixels for the depth (portrait ratio or square).
But make sure you are doing this on a copy not resizing your original image. I normally save any images destined for uploading in a separate folder then upload from there.
In reality, I use a different computer for photo work then transfer to my internet computer using a USB removable drive. This prevents any malware from infecting my main work equipment; but let's not worry about that sort of thing for now.
Try a few test items and see how you get along with this resizing method.