Learn Turkish: Tüm takım hazır. - The whole team is ready.

Tüm can mean "the whole" when used with a singular noun, or "all" when used with a plural noun. Here, tüm takım means "the whole team". If you wanted to say "all the teams", you would use the plural: tüm takımlar.

Where is the word for "is" in this sentence?

In Turkish, "to be" (am/is/are) isn't a separate word but a suffix attached to the final word. For the third person (he, she, it, or in this case, "the team"), that suffix is completely invisible! Because there is no suffix, hazır simply acts as "is ready".

Could I use bütün instead of tüm here?

Yes, absolutely! Bütün and tüm both mean "whole" or "entire" and are interchangeable in this context. You will often hear Bütün takım hazır used to mean exactly the same thing.

Since we are learning possessive suffixes, how would I say "Our whole team is ready"?

You would add the "our" suffix -ımız to the end of the noun. The sentence becomes Tüm takımımız hazır. Notice how the suffix follows the 4-way vowel harmony rule, matching the undotted 'ı' in takım.