If you don't need help getting started reading the portions of this manual that are most important to you, you should skip this portion of the manual.
If you are new to compilers, especially Fortran compilers, or new to how compilers are structured under UNIX and UNIX-like systems, you'll want to see What is GNU Fortran?.
If you are new to GNU compilers, or have used only one GNU compiler in the past and not had to delve into how it lets you manage various versions and configurations of gcc, you should see G77 and GCC.
Everyone except experienced g77 users should see Invoking G77.
If you're acquainted with previous versions of g77, you should see News About GNU Fortran. Further, if you've actually used previous versions of g77, especially if you've written or modified Fortran code to be compiled by previous versions of g77, you should see Changes.
If you intend to write or otherwise compile code that is not already strictly conforming ANSI FORTRAN 77—and this is probably everyone—you should see Language.
If you run into trouble getting Fortran code to compile, link, run, or work properly, you might find answers if you see Debugging and Interfacing, see Collected Fortran Wisdom, and see Trouble. You might also find that the problems you are encountering are bugs in g77—see Bugs, for information on reporting them, after reading the other material.
If you need further help with g77, or with freely redistributable software in general, see Service.
If you would like to help the g77 project, see Funding GNU Fortran, for information on helping financially, and see Projects, for information on helping in other ways.
If you're generally curious about the future of g77, see Projects. If you're curious about its past, see Contributors, and see Funding GNU Fortran.
To see a few of the questions maintainers of g77 have, and that you might be able to answer, see Open Questions.