If this is your first time looking for eyeglasses online, here is a general workflow to show you what it will take.
Get a Current Prescription
Although you don't need to get your frames in person, you will need to go for an eye doctor checkup to get a current prescription. An online prescription glasses retailer will require that you upload your prescription to the site before they fulfill your order. The site will use the prescription to cut custom lenses and fit them to your frames.
Set Some Constraints
With the wide variety of eyeglasses available, it can be helpful to set some constraints. For instance, budget is a good one. The frame shape also matters, and many retailers will suggest that you choose frames that contrast your face shape. Boxy frames work well for those with rounder faces, while they should be avoided for people who already have a very square jawline. By setting some constraints on what you're looking for, you'll have a much easier time at wading through the different options online.
Try On Glasses
This is an optional step, but some eyeglasses companies online will let you try out the frames using a dummy lens. They will ship a few pairs to you at a time, and you have a set number of days to try them on and then return them to the shop. From there, you can choose the frames that you like best and they will ship you back an eyeglasses copy with your correct lenses put in. This is a good step to take if you are not very sure about which style you like best.
Return to Your Eye Doctor
A final step that some people miss is that you should go back in to your eye doctor or an optometrist to get the fit of your prescription eyeglasses checked. The online manufacturer will cut your lenses based on the prescription, and this should include fitting the focal points of your lenses to the width that your eye doctor specified. However, there can be some unknown elements in the fit of your glasses, so you'll want to get them checked to make sure that the prescription actually sits in the center of your eye.
While it's not possible to get your prescription glasses done totally online, there is a lot of benefit of being able to try out glasses from a wider range of manufacturers online. If you have questions or concerns about using online eyeglasses providers, your eye doctor should be able to point you to some of the best services to use.