I planted five rows of garlic yesterday, thanks to the garlic fairy. The picture shows two rows of garlic laid out at the correct spacing, and waiting to be planted. (By the way, the correct terminology is that you sow seeds and you plant plants, but sometimes the two terms are used interchangeably).
Spacing is very important in vegetable and fruit gardening. If you plant (or sow) things too close together, plants crash into each other as they grow. Their leaves compete for light, their roots compete for water and nutrients, and instead of getting twice as many plants per row, you get less than half-size plants and your yield is poorer. On the other hand, if you space things too widely, not only will you get a lower yield per row than if you squeezed a few more plants in, but you leave lots of bare earth exposed between the plants, which will surely be exploited by weeds. Even if you can keep the weeds off the exposed areas, exposed bare soil gets eroded which you certainly don't want.
Remember, the soil is the key. If you attend to the soil and neglect the plants, you'll do OK. But if you attend the plants and neglect the soil, you'll have a disaster.
Garlic, apparently, should be grown in rows 12" apart (you can see how I've marked my rows with stakes and twine). Then you plant the garlic directly under the twine, 6" apart. Or if you want to be really space efficient you can plant the large outer cloves from each bulb 6" apart and plant the smaller inner cloves 4" apart. To be honest, I don't go along with a ruler measuring them, but I've a good idea what 6" or 4" looks like and I guesstimate. I also had three cloves of something called elephant garlic. The cloves were flipping huge, so I guess the bulbs must be downright enormous. The leaflet that came with them said to plant those 12" apart, so I did.
I'll weed these by hand for a while. I don't want a thick covering of weeds crowding out my lovely garlic. But if I use a hoe I might damage the garlic just underneath the soil. That's where the stakes and twine come in handy again - I can see where the plants should be, anything growing anywhere else is probably a weed (although plants do sometimes wander about a bit. I suppose rain and critters transport the seeds short distances). I'll leave the stakes and twine in place until the garlic starts coming up and I can see where the rows are, then I'll use them somewhere else in the garden. Another approach is to sow fast-growing seed, such as radishes, along the same line as the new plants. A green line of radishes quickly springs up showing you where to hoe and where to avoid. Within a few weeks you can take your crop of radishes and by then your emerging seedlings should be clearly visible.