1) 마셔 = drink it! 2) 보셔 = see it! 셔 is something like imperative, but we don't use like '보셔'. 보셔 is not wrong but we use like this '봐'. Likewise, we usually don't say like 하셔, but we say like '해'

according to TOPIK Test. 마셔 is informal form from 마시다 that means "drink". for another 셔, maybe it refers to talk about someone whom we respect to with another people to whom we can talk informally. for example: if we talk to another friends "my mom is a housewife" 우리 어머니는 주부셔