Case requirement for verbs
Is there a site where I can see what case a Polish verb needs? It's kinda hard to keep track of the case requirements for verbs. At least I know the basics, for example "być" needs the Instrumental case and ''mieć" needs the Accusative case.
As a general rule, you can assume that transitive verbs connect with Accusative for the direct object of the sentence. Although there are exceptions (for example verbs which connect with Genitive like "potrzebować", "szukać", "dotykać", "uczyć się"), such assumption is right most of the time. When negated they connect with Genitive. The indirect object is expressed in Dative.
Here you can find a list of verbs which connect with Genitive: https://www.duolingo.com/comment/12882227
You can also check syntax on Polish Wiktionary. Look at "składnia": https://pl.wiktionary.org/wiki/potrzebowa%C4%87
Wikibooks Polish course has a good guide to the declensions for the three genders.
That same course has a page called prepositions as a hint to declensions which I'm referring to several times a day at the moment.
To look up the declensions for individual words, use Wiktionary - it's an excellent multi-lingual dictionary.