You can find a member by searching using the AdminCP quick search in the upper right of your screen. You can enter their display name, email address, order ID, and more in this box to find members. You can also click Members in the AdminCP to get a general list of members. From here you can select to add a new member also if you wish to do so, which would then also contain the items for you to populate that you see when editing and existing member.
The edit member screen is split into sections on different tabs. Although most options are self-explanatory, there are some brief descriptions of what each of these are for below. (Note you may have more or less tabs than in the image below depending on the applications you have installed).
From here you can change the basic information required on a member account. These include changing a users display name, changing passwords or adding to Groups.
Note here that you can add a member to a main group and also add secondary groups giving you more flexibility over permissions than you would have with a single grouping. For example you may have a Sales and a Marketing section in your community with groups to match. You could easily set up some members to access both and others who can only access one or the other, simply by assigning the groups accordingly.
In this tab you can control restrictions on an individual member. Posting and approval before posting can be set indefinitely or for a set period of time. Controlling member restrictions may also be done from the front end by your moderators where permission has been given to do so and will update this area accordingly. You can read more about this here.
Whilst most members will generally fill in there own profile, there will always be times where a member has placed something you do not wish to be there (and therefore would like to remove), or needs something editing that they cannot. From here you can edit the members profile information such as changing there cover photo or editing there birthday.
This section is where system preferences can be changed or viewed that a user has set up. It not only comes in handy for changing these setting but also as a way of debugging problems on your forum that a member is experiencing. For example a user who's time is incorrect may not have the "Set timezone automatically" setting enabled.
There will come a time where you have members who are receiving notifications for things and feel they should not. Generally this is because they have set these notifications up and forgotten about them, or simply have left them on their default registration settings. Should the need arise you can change their notification settings from within this screen.
If you have more applications installed you will see some common settings for these are displayed within the members edit screen. This will allow you to quickly set up features for an individual such as allowing someone access to the gallery.
Other handy tools
Above the main area of editing you will notice there are a few other handy tools. Whilst these are self explanatory you will find one in particular quite a handy tool to have which is the "Sign in" button. This button will allow you to sign in as the member who is currently selected. Imagine you have a user who has a problem on the forum which you cannot see as an administrator. Maybe they cannot see a section in which you feel they should be able to view. This tool gives you the ability to see the community through the eyes of your member and effectively get to the route of the problem they are having. Once you are finished, you can easily log back in as yourself by clicking on your name and selecting "Switch back to yourname".
For information on setting up staff members, you can refer to the following guide within the moderating members set of guides