I often need to share a folder on one of my Raspberry Pi computers. Here is the process I use:

Install the software:

sudo apt-get install samba samba-common-bin

Check that the daemons have been started:

sudo service samba status

Make a folder to share:

mkdir ~/share

Add your share to /etc/samba/smb.conf

[My Share]   
comment=My Share   
path=/home/pi/share   
browseable=Yes   
writeable=Yes   
only guest=no    
create mask=0777    
directory mask=0777    
public=no 

Set a samba password:

smbpasswd -a pi

Restart samba daemons:

sudo service samba restart

Test it

Now you should be able to see your share over the network and log in using your user/password entered above.

Troubleshooting

If you cannot see the share, make sure that you have restarted the daemons and that they started back up. If you can see the share but cannot access it, check that the path you entered actually points to a valid location and that your user has the rights to access it.

The next step is to have a look in the log files which are located under /var/log/samba