There’s a “front” to every teabowl. You can find it by looking for the indentation or marking or painting on the bowl - that is the front.

If someone makes matcha for you, they will hand you the bowl with the “front” facing you. To show respect to your host, turn the bowl (spin it on your left palm, in 2 even turns), so the “front” faces them (it’s not polite to put your lips over the design). If there’s not a design to give you a hint, turn the bowl 2 turns anyways. Then drink.
How to hold the bowl:
1. Cup your left hand directly under the bowl (all your fingers are underneath)
2. Curve your right hand around the right side (no fingers pointing above the bowl)
3. Let your elbows be loose and out to the side

Raise the bowl to your mouth in this position. It should feel very comfortable and relaxed.

Drink all the matcha, in 3 1/2 sips, with the last 1/2 sip making a slurping noise to show your enjoyment of the tea. Then examine the beauty of the bowl before setting it down.