I have just bought a 1980 cx 500 it has sat in a warm dry garage for the last five years and it has 90,000 miles on the clock not fitted to start it yet going to change oil and filter new spark plugs ect
Wow, 90k miles is a lot. If the engine is known to be frozen from sitting or you just want to be careful, pull the plugs, shoot some PB blaster down the holes, and let it sit for a day or two. Then manually turn the crankshaft using the bolt on the front engine casing beneath the radiator. Lots of good articles/threads can provide the details.
Welcome to the forum. Please add your location and your bike's model and model year (NOT year first registered as UK paperwork shows) to your profile so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).
And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old and the Previous Owners may or may not have done the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. If it was parked for 5 years you should replace the tires no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid). And don't forget things like the rad hoses and the boot between the engine and swingarm (they can crack on the bottom where you don't see it).