you can grow many varieties directly in soil inside and outside the greenhouse. if outside check the variety is suitable.
A truss is a cluster of flowers from a single stalk. depending on the variety there can be as few as 5 and as many as 20.
when the flower has been pollinated the yellow petals will drop off and if you look into the green sepals [flower bud case] you should see a small pale green swelling. that is the baby tomato forming. at this point you can start watering with tomato fertilizer, following the dilution instructions.

If you know the variety you can look up whether its hardy or not (ie will grow OK outdoors)
Hardy ones will grow in the soil or growbags indoors or out. In either case they will need staking.