^^^ x2
The 12 point nuts do hold down the cylinder head. The screws with the internal hex's are studs which screw into the cylinder block. Afaik the internal hex is to allow the studs to be removed if required.
You could re-tighten the cylinder head nuts if you wish but it's not normally done once the cylinder has been retightened once after the engine is built at the factory or if the cylinder head gasket has been replaced. Personally I'd leave them alone, as one thing can lead to another...
If you do decide to retighten the cylinder head, you'll need a torque wrench that can measure the required torque ( a standard 1/2 sq. drive one should do) and a suitable 12 point socket to fit the cylinder head nuts. You should follow the procedure described in your Haynes shop manual. Essentially you start with the centre 2 nuts (there's 10 in total), loosen 1 of them by about 1/2 turn and then re-tighten to the correct torque figure using a torque wrench, then loosen and re-tighten the other of the centre pair of nuts. Then you move outwards to the pair of nuts either side of the centre pair (4 in total) Loosen and re-tighten each of these in an X manner. Then do the remaining 4 nuts (2 at each end of the cylinder head), loosening and then re-tightening each of these in an X manner. Only loosen one nut at a time and then re-tighten it before loosening the next nut. Don't loosen all the nuts at the same time or you might start an oil leak/coolant leak at the cylinder head gasket.
After you've finished, it's no harm to check the timing belt tension before starting the engine. If the timing belt has covered iirc more than 30,000 miles / 4 years, has any oil on it or you don't know when it was last changed, it would be a good idea to change it, plus check it's tensioner bearing.
If you click on the Search button at the top of the page, you can search e.g. Timing Belt - this topic has been covered many times in the past.
AL.