To connect to MUME server, you need to set correct remote server hostname (or ip adress), remote port and local port in Preferrences dialog. Then you simply run your favourite text-based MUD client (plain telnet, powwow, powtty, cancan ...) and connect to machine and port where MMapper is running. Your client connects to MMapper and it connect in turn to MUME server. All communication (client/MUME server) is passed by MMapper.
MMapper uses ANSI color mark to recognize room name in incoming text. So it is neccessary to set colour of look command in MUME to independent colour from others. You can do that simply by 'cha col all default', and then 'cha col tell yellow'. This is just an example. You can also choose another colour for look and then set different colour in MMapper Preferences dialog. Colour is represented with ANSI escape sequence without first ESC character. For example default setting is [32m, which means green color. If you use diferent color in MUME, set this ANSI sequence correctly. To allow MMapper detect room exits and terrain you shoud set your prompt, to provide such informations. This can be done via 'prompt all' MUME command.
Now you are ready to make first explorations and testing. I recommend you this: DONT USE YOUR MAIN CHARS until you get familiar with this mapper. There is base map included within distribution of MMapper. But only some main roads and good cities are mapped there.