You assign a name to a value in Mythryl using an equal sign:
#!/usr/bin/mythryl a = 10; b = 3; printf "a == %d\n" a; printf "b == %d\n" b;
When run this produces
linux$ ./my-script a == 10 b == 3 linux$
This looks a lot like C variable assignment. It is not, but for the moment it will do no harm to think of it as one.