Configuring the Makefile is pretty simple, and again we suggest that you look at existing examples before starting. Also, there is a sample Makefile in this handbook, so take a look and please follow the ordering of variables and sections in that template to make your port easier for others to read.
Now, consider the following problems in sequence as you design your new Makefile:
Does it live in DISTDIR as a standard gzip'd tarball named something like foozolix-1.2.tar.gz? If so, you can go on to the next step. If not, you should look at overriding any of the DISTNAME, EXTRACT_CMD, EXTRACT_BEFORE_ARGS, EXTRACT_AFTER_ARGS, EXTRACT_SUFX, or DISTFILES variables, depending on how alien a format your port's distribution file is. (The most common case is EXTRACT_SUFX=.tar.Z, when the tarball is condensed by regular compress, not gzip.)
In the worst case, you can simply create your own do-extract target to override the default, though this should be rarely, if ever, necessary.