Before you export your file as a JPG, you should save your file as a PSD file. This PSD file will be editable if you want to change something in the future.
Click on the "File" menu at the top left of your screen.
Click on the word "Save" or "Save As"
If you click "Save As", you need to tell the computer where you want to save the file and what it should be called.
Click on the "File" menu at the top left of your screen.
Hover over the word "Export" until options appear to the right of it.
Click on the "Export As..." link.
If you are going to put the file on your website, the JPG file should be under 2MB in size.
Look in the left-hand column to see what the size will be.
If it is over 2MB, then you need to lower the Scale or Quality a little but until it drops to below 2MB. Do this in the right-hand column.
Click the blue export button at the bottom of the screen and select the location where you want to save the file.