Do you want a veggie patch? Or flowers?
Hydrangeas are dead easy, plant them in half shade (preferably, in hot sun the flowers shrivel up, shade will work too), cut off the dead flowers in february. That's it.
Lavender is easy too, when the flowers are dead just cut them off. They say to never cut into the wood with lavender but we had an ugly one that we did cut back far into the wood and it grew back beautifully.
If you like roses, buy them. You can read a lot about the "proper way" to very difficultly cut them back but in the end just cut off the stalk of a dead flower. Cut the whole thing a lot shorter (easily take two thirds off) before winter. The "exact" way of cutting them back is too get an exact way of which way the flower grows. It all sounds soooo important but in the end if you cut everything off at the same height it will still grow pretty roses!
I put a fuchsia plant in the garden last year and forgot about it. Didn't do anything and this year it again flowered beautifully.
Butterfly bush is also nice if you like something with height. Just cut it back in winter when it's too big for your taste. That's it.
If you want a veggie patch I recommend growing courgettes at least. You can grow a plant from seed inside in march/april and put it in the garden in may or plant seeds/ready grown plants outside in may. Some flowers don't grow courgettes, those are the male flowers and the plant always starts off with that. After that it will grow flowers that have courgettes. Bell peppers work sort of the same way. You have to plant these plants again each year.
If you like herbs, sage, oregano and Rosemary are easy to grow and stay alive for years.
Don't be scared to cut things back, especially in march/april. This is just before it all has a growth spurt and many plants thrive by it. If they do die just buy new plants.
People can make gardening sound so difficult and specialised but it really isn't. You'll be a seasoned gardener within two or three years. Just cut stuff back if it needs a boost. If you don't like something change it or get it out and if you fuck it up just buy new stuff. You can't lose here.
A garden becomes a bit meh after a few years if it isn't fertilised. Fertilise it a couple of times a year just before it will rain (saves smell and it helps getting the nutrients to the plants).