There are two ways to do this.
MXCalendar - install via Package Manager
http://charlesmx.com/software/mxcalendar-revo.html
MIGx - install with Package Manager, then use ordinary resources and a Custom Manager Page to manage your events
http://rtfm.modx.com/extras/revo/migxdb/migxdb.tutorials/migxdb.manage-events-resources-in-a-cmp-with-help-of-migxdb
I always install MIGx as soon as I get my basic installation configured; it's so useful for so many things. MIGx uses the regular TV tables to store its data in JSON format; MIGXdb accesses other tables, such as the site_content table as in the case of the events tutorial, or your own defined custom tables.
The new documentation has a few bugs in it; the above rtfm page is best viewed with the latest version of Google Chrome. If the bottom of the page is hidden and won't scroll down in your browser, you can view the parts that are hidden using the links at the beginning of the page.