sent value of an annuity and when do I use the present value of perpetuity in a finance question( how can I recognize that I need to use one of these?...

When when do I use the present value of an annuity and when do I use the present value of perpetuity in a finance question( how can I recognize that I need to use one of these?) Likewise when do I use the present value of a growing perpetuity or growing a new entity and how can I recognize that I need to calculate this in the question?