Resizing photo to upload to website

I want to upload photos to my 'underconstruction website' but first I need to resize them. I have only a limited knowledge in this area. I have read and understood that the major issue in uploading the proper size is pixel width and height. Now someone has told me that the 'file size' also needs to be considered and compressed. I have a trial version of Paint Shop Pro.

In Paint Shop Pro, how do I properly resize the photos to upload, some need to be thumbnail size and others larger? And how do I be sure the file size is correct?

Thanks for your help

There are two ways of resizing: the first one involves the pixel size, while the second one involves the file size in kb.

For pixel size, find the command in Paint Shop Pro (the location is different among some versions) Image Size and enter the desired size in pixels, i.e. 400 x 300. You'll see on the screen if the size you entered will be ok for your site or if it needs to be bigger or smaller.
First resize the image to the desired pixel size and then, using the same method, create the thumbnail. This will leave you with two versions of the same image.

And for file size, you'll have to optimize the image. This will be according to the format, either .jpg, .gif or .png. You can optimize the file by going to File - Export - (format) optimizer. You'll then get a box with several options for you to choose from.
You can optimize the file after "pixel resizing" it.

Since this is the very basic of image resizing, I suggest that you take a look at the program's help file, so that you have a better understanding of what each command/option really means.

Sorry but I just want to point out the words pixel resize can have two meanings as in PSP's resample Using.
Always use "Smart Size " as the resample using mode. In this case PSP knows best.

Oh yeah, forgot about that... By pixel resize I meant to resize the file's dimensions, which are in pixels.