Assuming you have a the original hood design. It is like erecting a rig tent
1. Erect the hood bars
2. Clip the hood to the windscreen first.
3. Then attach to the rear.
If this is impossible/hard, then it maybe because the hood is very tight against the hood bars. If this is the case I suggest you invest in a pair of Hood Swivels as advertised in Miscellany.