Enter a file name in the File Name field and click on the Selected Only checkbox, and click on the Export button. Then set the size at something like 100 x 100 pixels. There are other options in this dialog box, but you can experiment with them later. OK the Bitmap Export dialog box. The JPEG Export dialog box allows you to adjust compression and smoothing.
Compression decreases file size, and speeds up downloading.
Smoothing rounds off jagged edges. I suggest sticking with the default settings here unless you have some compelling reason to experiment with them. Finally, OK the JPEG Export dialog box, and apply your background image to your web site. The tile I created in Figure 3 results in a reasonably subtle background image - and looks like Figure 4 when it's tiled behind a web page. Look for smooth, nebulous fills like clouds or rock surfaces.