I was wanting to know what type of plants would usually grow under conifer trees? In particular scots pine and yew.
Not many plants are happy there Aimeej - it's very dry and shady there. You could try Iris foetidissima, Geranium macrorrhizum, Liriope muscari and the vincas and ivies. It will help if you can enrich the soil with some farmyard manure or leafmould, and new plants will need regular watering in their first year.
Scots pines aren't as bad as yew. They tend to drop their bottom branches in time and don't have such a heavy leaf cover.
Honesty grows under my pines. Euphorbia robbiae grew under the yew for a while but there's nothing to speak of now. Try those and the ones Dove suggested and see how you get on.
If you can raise the canopy, ie chop off the bottom branches, your chances are greater but you still have dry and rooty to deal with so don't waste time and money on standard sun-loving perennials.