There are ants on the tip of my young avocado plant, and they've been there for a while now. I didn't know what to do. I thought they would go away after a while, but they don't. Is this a good thing or a bad thing? If I have to get rid of them, the method preferably should not involve going to the store to buy extra stuff.
It's not terribly clear what the insects are, but they look likely to be scale insect. The presence of ants (if they are there) would confirm that, because ants collect honeydew from the scale insect (also aphids), so you need to get rid of the scale and not worry about ants, they'll go on their own if there's no scale or aphids present.
If you're expecting to get fruit off this plant, then certain insecticide treatments can't be used, so you need something that kills the scale but is considered safe for vegetable/fruit plants. You can try spraying with neem or horticultural oil, but repeat treatments will likely be necessary. There's a thread here about ways to deal with scale on various plants which might be of some interest https://www.gardensalive.com/product/managing-scaleinside-and-out
Another thing you can do if the ants are ‘farming’ unwanted insects on your plant is to place sticky tape on your pot to stop them climbing.
An alternative method is to place baby powder, on the compost, on the outskirts of your pot. Ants hate the way it feels and should not return.
This will not affect your plant in any ways or form.
Bamboo is also correct on how to deal with unwanted insects he mentioned.