What is the difference between taxonomical aids Flora, Manual and Catalogue?
A Flora describes plants and where they live. Floras typically include a dichotomous key for identification purposes and often times will include range maps as well. Floras are almost always designed to be simultaneously regionally constrained and regionally exhaustive/complete (i.e., includes all plants that grow in that region or at least all taxonomic divisions of specified taxa). See Example.

A manual applies much more broadly to plants, and typically instructs you on a subject (e.g., identification/differentiation of species).  A manual does not need to be exhaustive and its scope is typically user defined (though often based on the scale/range of it's underlying subject). However, some have used the term manual to be more or less synonymous with Flora or otherwise similar document (e.g., see here). 

A catalog is simply a listing of all species organized in some way. These are usually alphabetical (vs. taxonomically organized like a typical Flora). You will also never find a key in a catalog and will often find less phytographic detail.

See Chapter 6 in Describing Species: Practical Taxonomic Procedure for Biologists by Judith Winston for further assistance.