It is simple to get started. Once you create an account, you add each of your financial accounts - bank accounts, credit cards, mortgages, property, etc. - by providing your log-in credentials for each. You are now ready to go. All transactions posted to any of the accounts you entered will be tracked by Mint and categorized. No need to manually enter transactions or to download activity. You can customize the categories as you like by creating new ones and tell Mint to remember a category for a given vendor.
You can also enter all your investments and brokerage accounts. This is one area in which Mint could use some improvements. You are able to track balances, transactions, and trends, but you will not be able to rely on it for any additional, meaningful analysis of your investments. Now that Intuit owns Mint, maybe they will at least get it up to speed with what is available in Quicken.
Keeping a close eye on the categories to which your transactions are assigned is key to making full use of Mint.com. I recommend setting up a budget for each category you plan to track income and spending in. Otherwise, at the end of a month amounts within a category not included in your budget will be left out of your budget summary and lumped into "Other." Luckily, when you review trends everything is included so this only affects your own analysis of how your income and spending compares to your budget.
Mint's mobile apps also come in handy yet also could use some improvement. The apps definitely serve as the quickest way to check account balances or see if recent transactions have cleared as well as to check how you stand on a budgeted category before buying that extra dessert at dinner or toy for the kids. One great tool in the app is the Cash Flow summary. You can quickly see whether you are living within your means for the month simply by opening the app. This can serve as a consistent reminder to live within your means and spend less than you make, the key to strengthening your own financial foundation.