If you are just starting to dip your toes into Magic, then buying boosters and playing sealed/draft is good because it can acquaint you with the set and card pool. It's hard to even know what you want if you only know 1 card out of 1000. But generally I prefer playing constructed, ie., making my own deck out of the cards I own at home and using the same deck over and over and tweaking it like an engine. With sealed and draft you open boosters and make a deck out of them on the spot, but once it's over you can't re-use it. You'd have to get new boosters and make a new deck next time.
Once you get well enough acquainted with the cards, you can just order singles online. Instead of paying $5 for a booster, possibly getting nothing you will use (although you might get a random real good rare), it's better to just spend five cents and get the specific card you want outright.