Calendar
Looking up to the cliff, you see the trees, and the sun shining down on them. Using the sun and the trees (up there on the cliff), you've devised a method to tell what time of the year it is, based on where the shadow from the trees fall. After a while, you develop a bigger system. This system is a whole calendar.
Look at the different shadow patterns. Know what they all mean. This is your very own calendar system.
れき
こよみ
None
Remember the word 歴史, which means "history"? Using a calendar, you too can remember history (otherwise, who knows when these things happened). So, the reading for this kanji is the same as the reading for 歴史's beginning, because they're related.
Make sure you make the connection between the word 歴史 and this kanji. If you do, it'll be much easier to remember the reading of this kanji.