@Rosemaryandlavender1 congratulations on getting started with your garden! I found your tiny cyclamen quite moving ☺️.
When I first started gardening, I did exactly what you are doing now: buying plants on a whim, without taking a wider view of how things would look together. But gardening is a lot like painting a landscape: things need to go together (or complement each other) in terms of size, shape, colour, density, etc. You need to put some structure in place (maybe using shrubs which give year round interest), then decide on flowering plants that will come together, or flower successively.
It’s rarely a good idea to have only one plant of a kind. You would be better planting groups of 3 or 5 (or six, to account for the one that will inexplicably die), otherwise your garden will not have unity and will not look serene.
Agapanthus needs full sun or it won’t flower. Tiarella needs full or at least partial shade. They just don’t belong together.
Rosemary grows well in poor, dry soil, with lots of sun, so maybe use that as a guide? You could try googling prairie style planting, with rudbeckia, heleniums, echinacea? Salvia Amistad would also work well, and flowers a long time.
I wouldn’t try to combine rosemary with any shade loving plants.
Any plant that you put in a pot will need a lot more TLC, as pots dry very quickly so you will need to have a habit of watering regularly (even every day in hot weather). Plants that are in the ground have access to a lot more moisture so need less watering.
There are lots of useful videos on YouTube, or you could watch episodes of Gardening World (fast forwarding all the bits that don’t apply to you). And there’s a very supportive group right here.
good luck x