Learn Italian: Hanno preso troppe decisioni senza di me. - They made too many decisions without me.

Preso is the irregular past participle of prendere (to take). In Italian, you do not "make" a decision; you "take" one (prendere una decisione). Since we are using the past tense here, "they made" becomes hanno preso (literally "they have taken").

Why is it troppe and not troppo or troppi?

Troppo (too much / too many) changes its ending to match the noun it describes. The noun here is decisioni (decisions). Because decisioni is a feminine plural word, troppo must change its ending to match, becoming troppe.

Wait, if decisioni ends in -i, how do we know it is feminine?

Singular Italian words that end in -sione or -zione (like la decisione) are almost always feminine. Remember that nouns ending in -e in the singular change to -i in the plural, regardless of their gender. You can clearly spot its feminine gender in this sentence thanks to the matching adjective troppe.

Why is there a di in senza di me? Doesn't senza already mean "without"?