When designing graphics for web, what resolution should I use?

The best resolution for web graphics is 72 pixels/inch.

How can I change the color of a dress in Photoshop in a nondestructive way?

It is presumed that your picture is already imported into Photoshop. Go to the Window tab at the top, click, and select 'layers' from the options, if 'layers' tab is not showing in the Photoshop window. At the bottom of the layers tab, find 'Create new fill or adjustment layer,' click and select 'Hue/Saturation'. Change the Hue by dragging the slider on the "Hue bar" to suit your preference. You can also check 'colorize' and adjust the hue. The adjustment layer can be hidden or made visible with 'layer visibility' or the "eye icon" of the layer to see the changes made.

How can I create page numbers in InDesign?

Note: Anything you insert in a master page will affect all the pages tied to it. By default, all the pages are tied to the A-master, and so anything inserted on A-master will appear on all pages. Once you have set up your document with multiple pages, check ‘pages’ from window tab if it is not pinned on the panels at the right side of the InDesign window. Open ‘pages’ and double-click on A-master to open the master page. Grab the ‘type’ tool from the toolbox or hit T to activate it. Click and drag to create an empty text frame on the master page. Go to ‘type’ and find ‘insert special character.’ Choose ‘markers’ and select ‘current page number.’ This will insert the character ‘A’ because you are now on the master page A. You can format the font by changing color and size. To see the effect, go the ‘pages’ panel and double-click on page1 or any other page.