Unless you can afford to buy a huge property with a solid fifty-foot-high wall around (and maybe a moat with crocodiles in it as well), you have to get along with your neighbours. So it's important to know what your rights are – and what your neighbour's rights are too.
You and your next door neighbours are each supposed to stay inside your property line, the invisible line dividing your land from the neighbour's land. Your neighbour has no right to plant even a few inches of her garden on your land and you have no right to situate even a few inches of your picnic table or toll shed on her land.
Sometimes neighbouring houses share a single-driveway, with the property line running right down the middle of it. You have an easement over your neighbour's half of the driveway, and your neighbour has an easement over you half. The easement gives each of you the right to drive from the street to the garage or parking space on your own property.
Neither neighbour can block the driveway, either permanently or temporarily. You can't build a fence on the property line. You can't park your car in the driveway unless and your neighbour both agree to this. You can't let your children leave their bicycles, doll collection, basketball hoop, and rollerblade ramp in the driveway. If you block the driveway, your neighbour can remove the obstacle (as long as he is acting reasonably and causes only a minimum amount of damage).
However, your neighbour can't force you to maintain or repair or even shovel the snow off your half of the driveway. If your neighbours want to fix your half of the drive, they come onto it to do the work. But they can't usually make you pay for the work. (Of course, it works the other way too, and you can't force your neighbours to fill the potholes on their half, either.)
Not just next-door neighbours but a wider circle may have the right to object to what you build on your property. Suppose you're putting on an addition or renovating or putting in a pool or constructing an outbuilding like a garage.
If it doesn't conform exactly to municipal zoning or other by-laws, you'll have to apply for an exemption from the by-law. Your close neighbours will be given notice of your application and a chance to oppose it. (If a neighbour does oppose your plans, you may be able to settle the objection privately).
And neighbours for some distance around have the right to complain to the municipality if you contravene by-laws against making too much noise, letting your weeds grow, operating a business out of your home, and quite a few other things.