Means a great deal on any bike, but especially on a single speed.
On the front (the chain ring) gear on the crankset, more teeth equals greater speed, but also greater pedaling effort. Fewer teeth means lower speed, but less pedaling effort.
On the rear, just the opposite. More teeth means lower speed and less peddling effort and fewer teeth means more speed and more pedaling effort.
On a single speed, you need to carefully analyze what you can handle as far as effort for the type of riding in your area. I'd visit with other single speed riders in your area and see what gear combos they are using.
Yes, the number of teeth does mean something.
But preferably, you need to look at BOTH the number of teeth on the chainring(by the pedals) AND the number of teeth on the sprocket(at the rear).
It's about gear ratios.
Ratio means you're trading one amount of movement at one place for amonther amount of movement at another place.
You can trade a long movement for a short movement, or a short movement for a long movement.
Speed for strength, or strength for speed.
Let's say you've got 44/11 (not very likely, but easy math).
This means the rear wheel turns four times for each turn of the pedals.
(44/11 = 4)
If instead you had 44/14, or 44/15, the rear wheel would only turn (about) three times for each turn of the pedals.
For the same stretch of road, that would require a lot less pedal pressure to push the bike forward at the same speed.
Now you can easily do some basic math and discover that ONE tooth either way doesn't make a huge difference.
But it's there.
Sometimes, even a small change is important.
The smaller a sprocket is, the more important one tooth change becomes.
Then, you probably have a sense of what gear combination you prefer to ride in for a given portion of where you ride ...
So, with an understanding of what north woods gal said, try to figure out what gear combination you most commonly use AND THEN decide if that is good for other occasions OR if you want to compromise with an easier-or-harder SINGLE front-and-rear combination.
The same ratio can be achieved with different combinations: