The green stuff Matcha, more than any other type of tea, is used as an ingredient in cooking. That is probably due to its distinctive flavour and the fact that it's easy to use. While dried tea leaves have to be brewed to extract the flavour, the leaves for matcha are ground to a fine, dust-like powder that mixes easily into other ingredients.
Good quality matcha has a vivid green colour and a little goes a long way, both as a drink and as an ingredient. In large quantities, matcha can taste bitter and grassy, although in some cases that can be desirable; in the Japanese tea ceremony, matcha is deliberately made to be very thick and strong.
Matcha is used to flavour soba, daifuku (sweet mochi), ice cream and baked products such as chiffon cakes, sable cookies, macarons and financiers.
If you want to use it in one of your own baked recipes, just mix in a small amount with the other dry ingredients - usually a teaspoon or two is enough. If you find it's not strong enough, increase the amount in subsequent attempts. If you use too much the first time around, though, the product might be too bitter. For custards, ice creams and confections, mix the matcha in with the sugar, so it gets evenly distributed with the other ingredients.