How do i slice a file?

Ok so I've built the ormerod... i did the ormaxis prints, worked great with the odd glitch.
But I've just gone to print the ormerod large-gear stl file and it always messes up...
either the nozzle pritns way too high or it just stops midprint...

heres what i did, am I creating and printing the g-code files correctly;
1. I open proterface/slic3r settings/ (i have the ormerod-0.5 settings loaded)
2. I drag over the STL file. Click 'export as G-code'. (some times it saves the file as a .g type some times it saves the files as a .gcode does this matter? if so how do i save as .g, do i just write .g after the file name?)
3. I add this file to the SD card...eject and put into the printer...
4. Re-open pronterface, click connect to printer.
5. I home the X, Y and Z (sometimes I prewarm the heat bed as this seems to take a while to get up to temp), click 'SD' and open the file with all the M557 corner location points in, press G32
6. On pronterface I click 'SD' and click on the 'large-gear.gcode' file.
7. it attempts to print....

any help would be MUCH appreciated!!!

hey!

I am also having troubles slicing a file...I always get stuck on the forth step

When I click connect to printer, I always get an error message like:

[ERROR] Could not connect to None at baudrate 115200:
Serial error: could not open port None: [Errno 2] No such file or directory: 'None'

I was wondering if you had to type in a port name before you could connect to the printer?

Thank you!