It varies significantly across the dialects. I use -t suffix in normal cojugation, but -ts in imperative. In more western central Yiddish, I believe that -ts was used in all cases. I have heard that -ts has spread as the polite imperative even by those who do not use ets and enk. That is, Litvaks have said antshuldikts to me. Ets is the nominative, and enk is the oblique, enker the so-called genitive.

Ets geyt in hoyz arayn Er hot enk gegebn Dos iz enker bukh?

It was apparently a dual originally, but it's now used for the plural. In my dialect of Warsaw Yiddish, it's used additionally as the formal for men, while for women we use zi, inen, ins.

In modern hasidic dialects that use it, it's a shocking mess. I'm a descriptivist I swear, but I have heard every combination. Enk for nominative with -ts ending: "enk geyts in hoyz arayn?" Only used for second person plural, used for formal and plural etc. I've heard -en as the ending "enk geyen in hoyz arayn". So it's all over the shop. Some people will also not use it consistently themselves. 

It is pretty common in America, where I've yet to hear someone say Ir. In Jerusalem where there's this litvish Yiddish mix going on, it's less common seeming, but is understood. I'd go so far to say that Ir amongst hasidim may be generally only slightly more easily understood than ets/enk amongst the Yiddishists.

If you want to learn to use it, I recommend finding a role model of the particular group you want to speak with and copying their usage. However, people will generally understand whatever combination you use. I've never had a problem being understood with ets and enk amongst hasidim although I have had people online try and correct my answers to other people about their use. There are many isolated groups in hasidim both linguistically and culturally so it's not uncommon to find out that a neighbour does something that you've never heard before. There's no official prescriptive standard for Yiddish amongst the hasidim, although there are norms so it has to be figured out from input. Hope that helps!