What you need is a Field Guide, a book of a size that can be carried
with you in a small pack or some even in a large pocket.
Field guides are limited by their size as to the number of plants that
can be identified, but most can get you to a genus, and then you can
search more thouroughly at home for species.
Field guides are limited to specific regions/areas of the US and can
usually be found in the nature section of a good bookstore.
Many states have Native Plant Societies that can direct you to guides
for your state, and some publish field guides.
What state are you in; someone may be able to recommend a field guide
for your state.
( I have probably 2 dozen various guides for California: desert,
Sierra, coastal etc)

Emilie
Nor Cal