Would you please elaborate on what you did and what result or error you received? Custom partition suggests that you tried to create your own partitions, which is do-able and can achieve better results than the default.
In GParted, I assume you first either removed or shrunk any Windows partition if you are dual booting. So beginning there.
You need to create a few partitions for Linux, at least two of them, one of which is a swap space. It should be about 2x - 3x the amount of RAM you have in the PC. Normally I put this at the end of the drive. You can create the partition and then set the type to Linux Swap.
Next you need to create the other partition / partitions that you want. I typically create a boot partition, which holds the Linux-images. I make it about 512Mb - 1Gb depending on my mood. Like with the swap space, choose the file system type, probably Ext-3 or Ext-4. Then you select the 'mount point' which would be /boot. I then create a separate root '/' partition the same way. Typically I give this about 40%-50% of the remaining space. Select the file system and mount point. Lastly I allocate the rest of the space to /home the same way.
If you are planning on running a server that has a lot of data in /var, you may or may not want to make that a partition. It really doesn't matter since the file system is flat anyway.
I think the big one is the separate home and root partitions that allow you to put updated, or other Linux distros on while keeping all your data.