As Bill220 said - but I would add that after you've tried fingers for a while, move on to try smaller glass toys. They are smooth and take very little lube to slip in easily.
Then find something tapered (like a butt plug) preferably with vibration. The taper will help you explore stretching to accommodate larger toys. Once my wife was able to handle a 1.5" diameter butt plug, she was ready to try anal sex. I'm a little larger than that - but with enough lube it works our fine.