OK Cmarsha, I'll walk you through this step by step:
Remember that amphib ops are VERY different from normal strategic movement via transports............
1. open the 1942 scenario and play as the British (Western Allies) for the following exercise
2. open the technology screen to see the level of your amphibious capaccity under your transport units
3. I think it is 3, this means that 3 units can cross a transport bridge to make an amphib assault (an armor unit counts as 2 units for this purpose, so, say you can amphib with 1 armor and one other unit.
You can and should increase this capability over time by "teching up" the amphib attribute of your transports.
OK, let's move some units!
Move say 5 transports into the sea zone between the Low Countries (careful NOT to move them through the narrows at Dover, as they will be damaged by the German artillery op-firing from Western France) and Southern Britain (England.) Use whatever bombers you have in ground strikes against the defending artillery, this will suppress the artillery and make them less effective against your men who are about to wade ashore. You can also send bombers supported by heavy fleets, hit yes when the game asks if you wish to use naval shore bombardment. your Heavy fleet will probably be damaged by the artillery in this exchange. Oveer time, you will master the art of amphib ops, like using a strong bomber to weaken a single artillery unit, then sending in other air units one at a time, each one "escorted" lol by a heavy oe even light fleet firing naval gunfire support - this combo can be very useful for weakening the defenders prior to your guys hitting the beaches..........
Now simply move an infantry unit from England onto the transports sitting off the Low Countries, then on to the Low Countries. Repeat this action with other ground units (since your amphib level is 3, you will be able to use 3 units.) Once you've maxed out your invasion force, bring in another heavy fleet and any remaining air assets you have at your disposal, even fighters can help just a little against the defenders. Since you need to have twice as many surviving attackers as surviving defenders to successfully occupy, this attack will probably fail - no surprise there. IIRC the German defend this place with like 2 inf and a artillery, maybe even a militia or armor, don't remember right now.
The point is that now you've made an amphib assault. Don't hesitate to ask other questions as you run into challenges. All the best and good luck!
Last note: no amphib ops can be conducted during winter turns in northern regions (weather.) You can see the northern regions more clearly by selecting the appropriate box in the options menu at the beginning of the game, I think it is called "cold regions" or something similar. Choosing this option makes cold areas look slightly "frosty" during winter turns.