Hi welcome to the wonderful world of gardening. 1 has to accept that odd non germination or the fact that some plants won't like your soil. If the plot is over hung with trees from a road side - as ours is - one has to plant with light in mind otherwise they go leggy towards the sun
Find a proper garden centre - take along a list of what you would like to grow and ask. If U have time, read the backs of seed packets. Grow what you will eat for the 1st 3 years, after which you will know your soil, how much sunshine you get - then it's time to experiment.
Gardening club - a good idea. Or your local WI, many will be gardening on a regular basis. Some garden centres run 'how to' sessions.
Raising from seed is the cheapest way to begin. A greenhouse needs shade from direct sunshine, an automatic vent to air the area and plants will need watering. That's early morning or at dusk.
If possible install water catchment barrels from the guttering.