Learn Polish: Czy to jest torebka mojej mamy?

Yes! It comes from torba (a bag). Adding the feminine diminutive suffix -ka literally makes it "a little bag," but in everyday Polish, torebka is the standard word for a woman's "handbag" or "purse".

If the base word is torba, why is the diminutive torebka and not "torbka"?

Polish often inserts an extra e to break up difficult consonant clusters like "rbk". This makes the word easier to pronounce. You will frequently see this extra vowel (often called a "fleeting e") appear when adding diminutive suffixes like -ka or -ek.

Why are mojej and mamy used here instead of moja mama?

They are in the Genitive case, which is used here to show possession, just like the apostrophe "s" in "mom's". The feminine nominative moja mama changes to mojej mamy in the Genitive.

Could I drop the word jest and just say Czy to torebka mojej mamy?

Yes, you can! In Polish, to can often act as "this is" all by itself. However, adding jest (Czy to jest... meaning "Is this...") is very common and sounds slightly more complete.