After This
From Now On, After, Since
noun
From after, just means after this or from now on.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
以後は、このアドレスにメールして下さい。
From now on, please email this address.
以後、気をつけます。
I'll be careful after this.
四月八日以後は、学校に行かなければいけません。
After April 8th, you have to go to school.