at one's fingers' (also finger) ends: nearby, close at hand; readily available or accessible; at one's disposal; (hence) within one's range of…

to get the hang of: to become familiar with the proper wielding or use of a tool; figurative to get to understand, manage, master, deal with as an…

to know one's onions: to be experienced in or knowledgeable about something.

In adverbial phrase inside out/ˌɪnsaɪd ˈaʊt/, formerly also inside outwards (usually with the verb turn): So that the inner side becomes the outer…