I would for a start:

- read a lot about makefile.
- read a lot about programming.
- write some small programs to make use of what you understood with previous reading.

At least, that will give you some understanding of how to fix your own errors.

Then, I would proceed to port things.

Some hints:
- some project do not make use of make but another build tool (cmake, ninja, etc...) which can make the port a bit more complex (ie: extract a working makefile from the build tool that will work with make).

- sometime there is a configure script that must be run before doing make. Again, you can run in various trouble here. Fun fact: sometime the configure script is larger than the whole project.

- sometime the configure script accepts arguments. You have to figure them out first.

- sometime the project is configured with a config.h (or other filename...) where you define optional things in.

- sometime MorphOS simply lacks whatever is needed to compile the program. For example, if the program relies on QT(4|5|6) or KDE GUI toolkit, do not expect porting the stuff without major PITA as you'll have to also port dependencies, or if the program is well architectured, write your own GUI with MUI...

- sometime, you'll have to modify the program to make it work by replacing some missing bits.

- you'll have to figure out the difference between libnix and ixemul binaries and how to compile things with or without -noixemul flag.

- you'll have to take care of license too. Some allows binary distribution without sharing your modifications, while some other licenses enforce source distribution.

All those things are the tip of the iceberg. Good luck soldier. You're about to enter an extrem minefield. :)