Ive used the Algeciras to Cueta twice, a few years ago now. Its a Spanish enclave so its a bit easier i reckon than Tangiers.
On the way to the ferry there were portacabins at the side of the road selling tickets for the crossing. They normally ask the cc of the bike your riding and charge accordingly.
The first time i did the crossing these booths selling the tickets were closed (due to the time of year) and i bought one outside the port carpark. There a plenty of ''helpers'' that will be eager for you to buy a ticket at their booth.
Once across the Straight and at the border you can get the help of a local to do the paperwork to clear the border. These guys normally have a id card round there necks and will assist you for a fee. If im teaching you to suck eggs i apologise, agree a price before using these helpers or things can get heated.
If you cant get Green Card insurance for Morocco you can buy it at the border crossing point.
Hope this helps