Hello and welcome to JustAnswer!
To set cam timing you start by rotating the crank until the key is at about the 1:00 position.
The crank sprocket is installed with it's mark at 12:00 and the intermediate gear's mark should be at 6:00, the marks on these two gears should line up. Install the gears and chains into the engine. Rotate the engine if necessary to install the sprockets yet keep the marks lined up. It is recommended to lock the crankshaft in place at this point.
Loosely install the left timing chain. It goes to the inner sprocket on the intermediate gear, run the chain up to the cams.
Route the chain around the left exhaust cam sprocket first with the sprocket removed from the cam. Have the sprocket so it's dowel pin hole is pointing near perpendicular to the valve cover sealing surface. Install the chain on the sprocket and turn it counterclockwise, making sure there is no slack in the chain between the crank and this sprocket. If your dowel pin hole isn't pointing at the 12:00 position in relation to the valve cover sealing surface when the slack is gone then move the chain on the sprocket accordingly.
Then route the chain over the left intake cam sprocket, making sure the dowel pin hole is again perpendicular to the valve cover surface and no slack is between each cam sprocket.
Then you can slide the sprockets on the front of the cams and start the sprocket bolts.
There is a hex on each cam where you can use a wrench to turn the cams one at a time to line up the dowel pins with their holes in the sprockets and slide the sprockets in place.
Then you can install the chain tensioner.
Go to the right side of the engine and perform basically the same steps, except this time you'll be starting with the intake cam instead of the exhaust cam.
Once you have all chains and tensioners in place double check all of your marks. The crank should be at 12:00 and intermediate mark at 6:00 and the marks should be lined up. All cam sprocket dowel pins should be pointing up, 90 degrees from the valve cover sealing surface. When the slack is out of the chains and you're happy with the installation then tighten the cam sprocket bolts.
Turn the crank two full revolutions and line up the crank marks again and double check the cam marks.