radare2 is not a source code debugger so you might see some things that are missing in comparison to what you got in GDB.
This feature is not implemented in radare2 and I'm not sure will be. Anyway, you can point
eip to the function you want to execute by using
dr eip=0x... but you'll have a hard time with passing arguments through the stack (although it is possible).
You can also check
dx? to see examples of how
dx should be executed. Check
gs as well to execute syscalls.
Also, you can use radare2 with gdbserver/gdb so you better check this out as well.
Here is a good place to read about migrating from GDB to radare2.