At the start, you are commanding 4 paratroop platoons that have landed with gliders (#1/2/3/4 on the map). These 4 platoons each have a specific ScriptID, which has consequences. #1 and #2 have orders to seize the upper bridge, #3 and #4 orders to seize the lower bridge (blue bridgeheads on map). If you would try otherwise and seize the bridges with the 'wrong' platoons, the mission objectives will not complete as the scripts expects the correct ScriptID's! Yes, I could have change this, but I didn't. Just follow the mission orders, right?

Once a bridgehead is established, an enemy counter-attack will occur. Be prepared! They're not that heavy but you don't want to be on the other side with just a single unit. 

Then most of the game happens on the western bank of the canal. You need to secure some positions in two towns, which will cause some more small counter-attacks. On the easthern bank of the river, you only need to hold that position. Apart from one or two small counter-attacks, that shouldn't be too hard. Beware for a surprise attack tho', keep your eyes open!