Hi gale65,
We can get you running Dirty Unicorns with No problem!
OK, first off Great choice on deciding to go with Dirty Unicorns as your custom ROM. I'm very confident that you'll impressed with it's stability, performance, features and how smooth and fast it runs!
So, just to clarify... You have unlocked the bootloader and have only rooted your N5?
You haven't installed a custom recovery like TWRP or CWM yet?
If yes... Then first you need to install a custom recovery like TWRP, CWM, or Philz CWM based recovery. Personally I do prefer TWRP because of the features... Charging while in recovery mode, OTG support, seperate EFS backups and more.
Custom Recovery's will allow you to create and restore nandroid backups and flash custom ROM's/kernels... etc.
To install a custom recovery is pretty easy, just follow the custom recovery section in Rxpert83's N5 Rooting guide here -
http://androidforums.com/nexus-5-all-things-root/790362-nexus-5-rooting-guide.html
If you already have a custom recovery installed or once you have one installed. Before you do anything else to your N5, you need to make a nandroid backup of you device and a backup of your EFS partition. This will allow you to recover your N5 to how it is right now, if something was to happen or go wrong. A nandroid is a snap shot of how the device is setup and you can restore to that setup easily. The EFS partition is where the phones IMEI/MEID, radio setting and etc.. are stored on the N5 and that's why it's important to backup the EFS partition.
Once the you make a the nandroid and EFS backups, it's best to not only save those on your N5, but you also need to save them safely off of the device on like a PC or hard drive, somewhere that they are accessible.
Once that's all done... Actually flashing and installing DIrty Unicorns is pretty easy.
Download the DU ROM and just one of the Gapps packages of your choice to your N5.
Reboot your N5 to recovery and perform a factory data reset/wipe, (depending on the recovery installed) just don't wipe the internal storage of the device.
Click Install and navigate to the DU ROM and select to install and once that's finished installing, flash the Gapps package also... Reboot and success!
That's the basics of it... Once we know which recovery your using, we can give you more detailed instructions and if you have any questions don't be afraid to ask.