Only-Way-4-Destiny!, you
have a choice - either bo hiu / bo chap your teacher, and don't
bother about drawing structures of compounds that you won't be
asked to draw at 'O' levels (assuming you *are* at 'O' levels...
are you?), or if you want to learn them, then self-educate (this is
the age of the internet - google be thy sword, wikipedia be thy
shield) yourself about Kekule structures, Lewis structures, lone
pairs of electrons, bond pairs of electrons dative covalent
bonding, etc.
You can also easily google the structures of any compound you
want. But it makes more sense, if you learn the underlying
principles, so you can make sense of the structure you google
out.
You may or may not understand the following (its ok if you
don't, it's not required at 'O' levels anyway... you *are* 'O'
levels, right? If you're 'A' levels, then you definitely must know
how to draw the Kekule and dot-and-cross structures that your
teacher tasked you), which is the reasoning and thought process
that 'A' level students have to do go through, in drawing
structures like the polyatomic nitrate(V) anion.
To draw the nitrate(V) or (NO3)- ion (it's recommended the
student draw the Kekule structure first, then translate to
dot-&-cross notation) :
1) First draw the central atom, N.
2) Then draw 3 O atoms, single bonded to it.
3) The fact that the anion is uninegative, means at least one of
the O atoms must be negatively formal charged.
4) In other words, that O atom must have 3 lone pairs and one
bond pair.
5) Hence, try drawing 1 single bonded O, and the 2 other O atoms
be double bonded to N.
6) But in which case, N has violated its octet. Being in period
2, it does not have empty 3d orbitals with which to expand its
octet.
7) Consequently, you realize that 2 of the O atoms must be
single bonded (ie. each with 3 lone pairs and 1 bond pair).
8) Consequently in turn, you realize that the N atom must have a
postive formal charge, because
8ai) you have 4 bond pairs for N, ie. 4 valence electrons near
the nucleus of N, and indeed, N is in Grp V (ie. 5 valence
electrons for no charge); so the N atom should
indeed have a +ve formal charge.
8aii) the entire anion is uninegative, and since 2 of the O
atoms have a -ve charge; so to cancel out the 2nd -ve
charge, the N atom should indeed have a +ve formal
charge.
8b) Since (ai) and (aii) agree with each other, this supports
the validity of your Kekule structure.
9) Your N atom has trigonal planar electron geometry with
sp2 electron orbital hybridization.
Once you've drawn your NO3- anion, with individual formal
charges inside the brackets, and a overall uninegative charge
outside the square brackets; draw the unipositive Na+ cation,
also with square brackets. The electrostatic attraction
between the cation and anion represent ionic bonding. So obviously,
sodium nitrate(V) has ionic bonding between the cation and anion,
but covalent bonding within the anion.
Hope you had fun. Everyone loves Chemistry! 
