Alter Ego

In order for the OS to share folders, you need the Samba package; which is not installed by default. Using this step-by-step guide, you will be sharing folders to other PC on your network in no time (no matter what their OSes are).

1. Install SAMBA

You guessed it:

sudo apt-get install samba

2. Fire up Nautilus, right click on the folder you want to share and choose Share Folder.
3. Choose 'Windows Network (SMB)'. Fill up the other details if you need to.
4. Click OK.

And you are done!

Oh, if you need to check what folders you are sharing:

1. Fire up Nautilus. Click on this icon.
2. Type in smb://localhost and press Enter (you can use the same method to view shared folders on your network; just replace localhost with the server's IP)