In Chapter 22, readers observe the developing friendship between Pip and Herbert. After a long conversation in which Herbert tells Pip of Miss Havisham's past and her upbringing of Estella, Pip asks Herbert about his means of income. Herbert replies that he is "A Capitalist--an insurer of ships," and tells Pip of his plans to trade "To the West Indies, for sugar, tobacco, and rum. Also to Ceylon, especially for elephants' tusks." When pressed, though, Herbert admits that he hasn't yet begun insuring, and adds, "I am looking about me." By this response, Herbert essentially means that he is constantly looking for money-making opportunities around him, as he isn't profitting from his work at the counting-house.
This phrase seems to be an interesting way of saying that they are looking for something useful to do with their time, like a career or hobby, or some small way to stay busy and earn some money for themselves. Gentlemen, meaning, men who had money that they didn't really work for, had a lot of time on their hands, and so Pip and Herbert were discussing the merits of finding something to do with their time. "Looking about" seems to imply that they haven't decided what to do, and were fine with that. Pip asks Herbert if he has actually embarked on the various ventures that he was discussing, and Herbert said no, that he was still "looking about," meaning, he hadn't decided and hadn't committed. He could have gone into shipping, or trading, or accounting, but hadn't committed and was still looking around for something, and keeping his options open.
Looking about is a luxury that the wealthy could afford at that time; they had a lot ideas and schemes of things to do with their time to be useful, but rarely acted on them. This is how Pip and Herbert end up wasting a lot of time and money. I hope that helps; good luck!