Well, you have to know what case is needed with a given verb, or a preposition. "szukać" needs Genitive, so "mała torba" is in Genitive.
I don't think there's a better way to learn this than just to learn by heart... You will make mistakes, of course, but at some time you will just know.
Well, there are rules about whether a genitive takes -i or -y.
The most important rule is that nouns ending in -ga or -ka have their genitives in -gi or -ki. Many of the fem. nouns encountered in this course end in -ka, so you get to see a lot of -ki genitives.
This goes some way to explain why "torba" -> "torby" but "torebka" -> "torebki" as mentioned in Jellei's response just above this conversation.
Well, 'thou' is(was?) informal on the T-V distinction line, so I didn't want to presume… ;) True, though, that I forgot that 'you' is relatively new to English – I should have used 'Ye'. :P
Yeah, I know – I'm pretty sure I never heard 'to seek' used outside of military contexts. Nevertheless, we have a lot of non-native speakers taking the course, so some less natural options end up on the list of accepted answers too…
Hide-and-go-seek. The children's game that is the only (off the top of my head) example of the use of seek. The counter counts, and rest of the kids hide. When the counter is done counting, they shout "Ready or not, here I come" and procedes to find the others. Even in this game, seek is mostly just in the title. As a native speaker, I tend to use 'find' or 'search' or 'look for' before 'seek', however if it is about Quidditch-Harry Potter, then it is Seek, :)
"We seek him here, we seek him there, Those Frenchies seek him everywhere."
I think it would help learning a lot if when you click on a word it shows not only the meaning but also gender, number and case (and ideally even the root word). I made zero headway with the grammar despite reaching this point which expects quite a lot of grammatical knowledge. Eventually went and bought a book instead