Filters is an essential feature of Gmail that compliments Labels to better organize your emails. Here I try to help you on how to get the most of this cool feature in Gmail.
As the name says Filters can be used to filter out your emails based on a certain criteria. The criteria can be like where the email came from, whom the email addressed to, having certain words in the email subject, having or not having certain words in entire email.
You can create a new filter from Setting > Filters > Create New Filter
Use Test Search to make sure your filter criteria is fetching only those email you expected. Now click on Next Step to see the Options of what you can do after filtering those emails meeting the search criteria.
You may prefer to Archive them, mark them as Read mail, assign a Star, apply a Label (this is really cool), Forward it to another email address (quite useful if your office does not allow accessing Gmail, you simply forward to your office email address those important emails) or Delete them. You also have an option to apply the filter to any existing emails that meet the filter criteria.
If you combine the power of filters with Gmail aliases, it will be very easy to organize your email and especially filter out any spam from Inbox. When you fill online forms to subscribe / register on various web sites, use your Gmail alias and then create a filter to apply a label to the email sent to that alias and also prefer to Archive it. This way you can avoid unwanted or not so frequently used emails appearing in the Inbox instead have them moved to a folder (aka Label).
This powerful combination of Filters & Labels makes your life easy in organizing your Gmail mailbox.

