Does the gro have marriages on the website I can't seem to find them or do I have to stick with local registry offices
Depends what you mean. The GRO does not have images of any registers or certificates online.
It does has a searchable index of Birth and deaths (though not a complete index of all births and deaths that may be ordered through the site).
If you want to order a marriage through the GRO you need to look up the GRO reference using a third party site such as Freebmd, FindMyPast or Ancestry etc. Then order the relevant certificate from the GRO site.
Use the same process for births and deaths outside the GRO's online index.
Cheers
Guy