Learn Italian: Ci vogliono due tatami per praticare comodamente. - You need two tatami mats to practice comfortably.

The verb volerci (meaning to take or to be necessary) agrees with the thing that is needed, which acts as the grammatical subject. Since due tatami is plural, you must use the plural form ci vogliono. If you only needed one mat, it would be ci vuole un tatami.

Why doesn't the word tatami change its ending for the plural?

In Italian, foreign loanwords generally do not change their endings in the plural. You say un tatami and due tatami. The plural is shown by the number due and the plural verb ci vogliono.

Why do we use per before the verb praticare?

When an infinitive expresses the purpose of an action (meaning in order to), Italian uses the preposition per. Here, per praticare literally means in order to practice.

How does the word comodamente relate to the adjective for comfortable?

Adverbs of manner are usually formed by taking the feminine singular form of an adjective and adding -mente. The adjective is comodo, so you take the feminine comoda and add -mente to create comodamente (comfortably).