During the winter season, climate doesn't normally allow any outdoor sports in most countries, at least in Europe. That's when the indoor season starts for the decathletes as well. Of course, indoors you can't practice all the events, e.g. it would cause some problems to throw a discus or javelin. That's why the number of disciplines is reduced from 10 to 7.
Heptathlon events are in the following order: 60 m - Long jump - Shot put - High jump - 60 m hurdles - Pole vault - 1000m
The World Record for indoor Heptathlon is held by Ashton Eaton. He scored massive 6645 points in Istanbul 2012. The European Record for indoor Heptathlon is held by Kevin Mayer. He scored awesome 6479 points in Belgrade 2017.
Every year there is either a World or a European Championships, mostly carried out in early March.