If you buy small plants from a garden center it will get you started easier this year.
Peppers, chillies, cucumber, courgettes, tomatoes etc all grow well.
Most of the above will need supported when they have grow a little.
Salad , like lettuce, salad leaves etc are really good if you eat that kind of stuff, you then don't have to buy any at the supermarket that go off after a couple of days. Just pull off the leaves you want to eat and the lettuce will keep growing once it is a reasonable size.
Also herbs like parsley, basil etc grow well.
I tend to find putting seedlings into decent sized pots straight off works well. Also thiings like herbs and lettuce can be put outside once they have grown a bit. The greenhouse brings them on faster.
If it is sunny during the day you will need to leave the door open or roof vent. As you will fry whatever is in there.
Also most things will need watered each day.