The share registry maintains the share register (the register of...

The share registry maintains the share register (the register of all shareholders) on behalf of the company. They record all share transactions too. They also generally handle things like voting for Annual General Meetings and Extraordinary General Meetings (you can usually vote to the motions as per the notice of meeting online) and also share purchase plans. Usually they provide holders with the offer documents and handle the payments for things like dividend reinvestment plans, share purchase plans, entitlement offers, optional off-market share buy-backs, capital returns and so on.

It is important to keep your contact details up to date at the share registry, especially if you want to participate in things like dividend reinvestment plans if offered by the company. You do this by having an online account with the registry so you can log in with your account credentials and update your preferences. It is especially important for most Aussie investors as you need to lodge things like your tax file number, self managed super fund details, with the registry so you don't get subjected to withholding tax on dividends.

The share registry also sends out holding statements summarising of any movements in your stocks (buys, sells, etc) during the month and sometimes you will need to access the holding statements online for the purpose of tax audits, etc.