Learn Finnish: Keltainen bussi odottaa kadulla. - The yellow bus is waiting on the street.

Finnish doesn't have a separate continuous tense like English does. The single verb odottaa can mean both "waits" and "is waiting" depending on what makes sense in the situation.

The dictionary word for "street" is katu. Why does it change to a 'd' in kadulla?

This happens because of a Finnish spelling rule called consonant gradation. When you add certain endings like -lla, a single t often softens into a d. So, katu becomes kadulla.

Why do we use the -lla ending for "on the street" instead of the -ssa ending?

The -lla ending usually translates to "on" or "at". If you used the -ssa ending (kadussa), it would mean "in" or "inside the street", which would imply the bus is buried under the pavement!

I learned that "I wait" is minä odotan with one 't'. Why does odottaa have two?

This is consonant gradation again! When you add the -n for the "I" form (odotan), it triggers a change that weakens the double tt to a single t. The "he/she/it" form (odottaa) doesn't trigger this weakening, so the strong double tt remains.