You get your first set of glasses about the time you get your first set of jowels ;o)
You will probably get them in the drug store or Wal-Mart for about 15-20 bucks. You don't need to go to the optometrist for these because he'll just screw you out of a few Jacksons and give you what you could have gotten for yourself anyway.
The sign says "Try to read this from about 14 inches away and the first line you have trouble reading is the strength you need".
Trouble is you can't read any of them easily. Does this mean you need 2.75 diopter? Who thought up this test?! A lunatic? What exactly does "trouble reading" mean here? It's so ambiguous as to be useless.
Therefore, just try on any and take the first pair that "sings to you". That is, you're on your own. Get the lowest strength first.
And beware of real cheap glasses. All lenses are not created equal. Imagine your car window. What if you could see straight out the front just fine but when you looked over to the side everything was distorted. Is that a decent window? Well you get the same crap with lenses. Move that eyeball around & check out the whole lens. Pay the man. A few extra bucks will save you many headaches.
You will need two sets of glasses (at least). A strong one for conventional reading and a weaker one for your computer. The reason here is that you sit farther away from your computer ... and ... the weaker one will let you focus on this greater distance. It is better for looking around in stores, etc. also. Don't let someone sell you a special set of computer glasses. This is just another way to shake loose a few more bucks.
Some odd facts
Once in a blue moon, you will be able to read normally (like a teenager). This has happened to me twice in the past ten years. It lasts for maybe a half hour. I think it's just because your eyeball gets randomly distorted (for whatever reason) and it just happens to cancel your inability to focus.
When this happens take advantage of it and read everything you can get your hands on. Read the small print. It's a real "kick". The second time this happened to me, I was driving down the freeway and had to steer & read at the same time ... very dangerous ... but it's got to be done ;o)
If you forget your glasses and absolutely have to read something quick, you can make a lens with your fingers and read one word at a time. Put your thumb, index finger and middle finger together to form a little hole. Look through this hole and make it smaller and smaller until it turns into a circle ... then you can read fine print, prices, signature and info boxes on forms and the like. It's very easy to do but you look like some kind of moron because other people (most people) don't understand that you can do this. [You have to put your hand against your face too.] It's a matter of physics ... the way light bends around the edges of small holes.
Oh yes. I'm blind in one eye so I guess if you have two eyes you better close one. If you try this with one hole for each eye, i.e. (eieio) use two hands against your face ... you'll probably get hauled off to the "bin" ;o) ... And you wouldn't be able to "microscope out" anything that close with two eyes anyway.