what is the meaning of molecular level and is molecular level is a microscopic level and how we study the structure of organisms at molecular level...

Biology is organized in a hierarchical system. From
largest to smallest, the list would go something like
this:

Ecosystem

Population

Individual

Organ
System

Organ

Tissue

Cell

Cell
Organelle

Molecule

Atom

For
more detail on what each level is comprised of, see the link
below.

Generally speaking, most microscope work is done at
the tissue, cell, or cell organelle level. Molecules are usually too small to be studied
with a microscope. In order to do research at the molecular level, scientists have had
to devise a variety of techniques, including tagging specific molecules with radioactive
isotopes, separating molecules via electrophoresis, western blot, or chromatography, or
doing spectroscopic analysis.

The science of biochemistry
is entirely devoted to studying the chemical reactions carried on by living cells;
biochemists are therefore working at the molecular level. It is a fascinating field
requiring a lot of theoretical knowledge, as things must be studied indirectly rather
than by direct observation.