Browning is a fundamental technique that all home cooks should master. One reason to brown is that it is esthetically more pleasing to see, for example, browned meat is more pleasing to the eye than meat that is grayish color.  Second it adds more flavor to the food. It can also burn off any excess fat. And in the case of ground food like meatballs, it also helps hold its shape so it does not fall apart. 

Note:  We find that you can use a non stick pan but a regular (e.g., stainless steel pan) works best. 

To  brown, first heat up a skillet or frying pan on medium high heat. Depending on what you are browning will determine if you need to add fat (e.g., oil, butter) to the pan and how much.  If using oil, the oil should be shimmering (ripples) showing it is hot. If using butter, you should use half butter and half oil to keep the butter from burning and again, it will shimmer when ready.  It will be rare to not use any fat to brown, except in case of very high fat meats.  Once the pan is hot and the fat is shimmering you can then start to brown your food.   You should rotate your food to keep one side from burning and to make sure it is browned evenly. If  you cook too long on one side it may burn and the food will cook unevenly.  For items like steaks, you can use tongs to hold the meat to brown the sides. 

Regarding Oil:  You can use olive oil or vegetable oil but if using olive oil be careful if you heat it too hot it will smoke.  Using part oil and part butter is a great mix.

Browning Meatballs: With meatballs I put a very small amount of olive oil in the pan.  I tend to use 73-80% beef (moister meatballs) so you do not need a lot, as the fat from the meatballs will gather in the pan.  Use 2 utensils to rotate the meatballs. 

Browning Veggies;  I typically use olive oil and butter but you can use vegetable oil and butter too.