The existing answer is great, but since you are feeling confused about the two functions of lo, I am going to write a supplementary answer.
If you see it in a sentence, without "que", it's a plain old pronoun. Examples:
- Préstame tu libro, por favor. Prometo leerlo rápido.
Lend me your book, please. I promise to read it quickly.
-- ¿Dónde está mi lápiz? ¡No lo encuentro!
-- Está en la mesa, junto al cuaderno. ¿No lo ves?
"Where's my pencil? I can't find it!"
"It's on the table, next to the notebook. Don't you see it?"
But if you see it with "que", then it's like in your sentence ("Ama lo que haces"). Examples:
Lo que no entiendo es el tercer problema de página 127. | What I don't understand is the third problem on page 127.
Creo que entiendo lo que propones. | I think I understand what you're proposing.
As @mdewey commented, it can be helpful to think of it as meaning
I think I understand that which you're proposing.