Both Uses of

accord
in
The Great Gatsby

Once there they were introduced by somebody who knew Gatsby, and after that they conducted themselves according to the rules of behavior associated with amusement parks.
p. 41.6

according to = in keeping with

He hadn't once ceased looking at Daisy, and I think he revalued everything in his house according to the measure of response it drew from her well-loved eyes.
p. 91.6 *

Definitions:

(1) (accord as in: according to, or in accord with)
in keeping with; or in agreement/harmony/unity with
This meaning of accord is often seen in the form according to or accordingly where it can take on more specific meanings. For example:
- "According to Kim, ..." -- as stated by
- "To each according to her ability." -- based upon
- "Points are scored according to how well they perform." -- depending upon
- "The dose is calculated according to body weight." -- in proportion to
- "We got a flat tire. Accordingly, I pulled to the side of the road." -- because of what was just said; or as a result
(2) (accord as in: reached an accord)
an agreement

In this sense, accord can refer to a formal agreement (such as one written between two countries) or an informal agreement (such as an unvoiced consensus about what should be done).
(3) (accord as in: done of her own accord)
mind

This sense of accord is typically seen in the form own accord or one accord.
(4) (accord as in: accord her the respect deserved)
to give someone special treatment -- especially respect