Do Certificate of Higher education students have their own graduation ?

It depends upon the school, but in my experience the gowns and such are only used for graduates receiving a degree.  Those receiving a certificate (I earned one many years ago) have a separate ceremony, which is nice, but doesn't use gowns.

The other answer is wrong, as I happen to know you go to a college of the University of London.  Unfortunately I didn't get to this question earlier.  Yes they do have academic dress for CertHE so I assume it will be worn at the ceremony, though you need to hire it.  There seems little point in defining it if nobody will ever wear it.

The academic dress for CertHE as defined in the university's regulations is as follows:

Gown:  Black gown of the Cambridge BA shape gathered at the forearm with button, cord and pleats.

Hood:  Black, full shape, edged with a red, white and blue twisted cord on the cowl.

Hat:  Black mortarboard.  (This might not be worn at the ceremony - you'll be told.  Rejoice if you don't have to wear one as they are the very devil to stop falling off - ladies are advised to bring hairgrips!  Men are unlucky as in my experience, they are required to doff their hat to the Vice-Chancellor or whoever else is presiding, so pinning it on isn't an option.  When I got my London BD, I was required to take it off as I walked across the stage to the VC and that had to be with my left hand so we could shake hands, exchange a quick congratulations and thank you, then I walk off.)

You will need to hire the kit from Ede & Ravenscroft and you get details about that, and how to collect it on the day.  Their staff will help you put it on.  The hood is always the difficult bit as it mostly hangs down the back.  The gown is open-fronted, it doesn't hook together like American academic gowns, so what you wear underneath will show so you want to go in something smart.  Men should be in a dark suit, white shirt and tie, and the neckband of the hood should be hooked under the tie.  Women should go for something similar - white shirt or blouse, dark skirt or trousers, and dark jacket if you like.  And it might be helpful to know that the gown sleeves end at the elbow.