You can append to your PATH in a minimal fashion. No need for
parentheses unless you’re appending more than one element. It also
usually doesn’t need quotes. So the simple, short way to append is:

path+=/some/new/bin/dir

This lower-case syntax is using path as an array, yet also
affects its upper-case partner equivalent, PATH (to which it is
“bound” via typeset).

(Notice that no : is needed/wanted as a separator.)

Common interactive usage

Then the common pattern for testing a new script/executable becomes:

path+=$PWD/.
# or
path+=$PWD/bin

Common config usage

You can sprinkle path settings around your .zshrc (as above) and it will naturally lead to the earlier listed settings taking precedence (though you may occasionally still want to use the “prepend” form path=(/some/new/bin/dir $path)).

Related tidbits

Treating path this way (as an array) also means: no need to do a
rehash to get the newly pathed commands to be found.

Also take a look at vared path as a dynamic way to edit path
(and other things).

You may only be interested in path for this question, but since
we’re talking about exports and arrays, note that
arrays generally cannot be exported.

You can even prevent PATH from taking on duplicate entries
(refer to
this
and this):

typeset -U path

PATH pre-populated

The reason your path already has some entries in it is due to your system shell files setting path for you. This is covered in a couple other posts: