It depends upon the context. It could be used in a literal sense, as in "chase after and capture them" (a command you'd issue to a police task force, for example) or "go and retrieve these objects" (a command you'd give to a dog or perhaps a group of children after you've thrown a bunch of objects into the distance). Sports coaches (particularly in football) might give their team a pep talk and encourage them to "go get them," which means "do your best in defeating the opposing team." A sales manager might encourage his staff to "go get them," meaning work hard and make a lot of sales.
Student or Learner