An agent acts for the insurer (the principal). What the agent can bind the insurer to depends on the agent's authority:
Express authority: written in the agent's contract with the insurer.
Implied authority: not written, but reasonably necessary to carry out the express duties, based on law or custom. Example: collecting the initial premium and delivering the policy.
Apparent authority: authority the public reasonably believes the agent has because of how the insurer presents the agent, for example by supplying forms, rate books and company letterhead. The insurer can be held to acts within that appearance.
Express plus implied authority together are called actual authority.
Fiduciary duty: premiums an agent receives are held in a fiduciary capacity (Ins. Code §1733). Keep them separate from personal money (no commingling). A person who diverts premium funds to personal use is guilty of theft.
Agent vs. broker: an agent represents the insurer; a broker acts on behalf of the client.