There are no function keys on the NeXT keyboard. If your application depends on function keys, you can modify the entry in the "a_termcap" file to cause other keys to simulate function key behavior. Modification of the "a_termcap" file is discussed in detail in Chapter 4 of the User's Guide.
For example, to use the escape key followed by a number key to simulate a function key, you would enter:
:k1=\E1:k2=\E2:k3=\E3:k4=\E4:k5=\E5:k6=\E6:k7=\E7:k8=\E8:k9=\E9:k0=\E0
When this line has been added to the "a_termcap" file entry, function keys 1 through 10 are emulated. For function key <F1> you would press <esc> and then press <1>, <F2> would be <esc> and then <2>, and so forth.