Ashley, take a look at the information on the back of packets of seeds in the garden centre. That will tell you whether the plant will be an annual or a perennial, the eventual height, spread and flowering season.
And don't panic! It seems complicated to start with, but you'll soon get to know the plants. Yes, look them up on a website by all means - I'd recommend the RHS website too, rather than a garden centre's website, because the RHS isn't trying to sell you anything. You ask "what's right and what's wrong?" Plants don't always fit into neat categories - it's worth learning what the basic descriptions mean, like "hardy", "tender", "annual", "biennial", "perennial", "deciduous", "evergreen", "conifer", "shrub" etc. Then you can understand that a Larch tree, for example, is a "deciduous conifer" (loses its leaves in winter, has cones), or that a Canna is a "tender perennial bulb" (won't survive the winter without protection, but will grow again next year from its underground food store if you protect it from frost). The more you have to do with plants, the more you'll learn about them.
Since 2019 I've lived in east Clare, in the west of Ireland.
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What about borrowing some books from the library? The more you read about plants the more it will stick in the mind.
We did tell you all this when you posted the same sorts of question in September last year.
You ask "what's right and what's wrong?" Plants don't always fit into neat categories - it's worth learning what the basic descriptions mean, like "hardy", "tender", "annual", "biennial", "perennial", "deciduous", "evergreen", "conifer", "shrub" etc. Then you can understand that a Larch tree, for example, is a "deciduous conifer" (loses its leaves in winter, has cones), or that a Canna is a "tender perennial bulb" (won't survive the winter without protection, but will grow again next year from its underground food store if you protect it from frost). The more you have to do with plants, the more you'll learn about them.