Hi,
I have really small garden that is on the 45 degree angle. Since I want to level it by putting more soil I would first need to build "support" wall from 4x4 (I think it's 4x4) posts.
Does anybody have an idea how to make the wall (4x4) solid in order not to fall down from soil presuure?
Maybe there was easier way to ask but I am new at this and I hope you understand what I need ;-)

Thank you!

The higher you go, the sturdier it need to be. If you are not going too high, you maybe able to use 8' landscaping timbers as posts. They have almost as much wood as a 4x4, but cost about half as much. I would put a post every 4' sunk 3' into the ground. Tie the ends to 3' posts sunk all the way in at the top.

Be sure and make the wall as tight as possible. Otherwise dirt will continually wash out, and you will need to add more. You can pack clay subsoil from the top part against the wood.

@labman,
Thank you, you are my big helper but I want to ask you one more thing.
I've seen that people are making the support walls without any vertical posts, the only stuff what you can see is horizontal posts (wall). How?
The reason I'm asking this is it's going to look a little bit ugly from the deck.
I was thinking if I can make it without vertical ones, just "flat" wall, I'd paint it or decorate it somehow.

Thanks!

How old are the walls you have seen? Dirt keeps pushing outward on a wall. Most eventually fall. I have seen walls made of horizontal timbers nailed to each other. Sloped back a little they may last for a while. My neighbor has a low bed with the popular vertical timbers side by side. It is 5-10 years old. As a nice spring day, I was looking around my back yard. I noticed how badly the timbers were leaning back.

The more support you give your wall, the longer it will last. You could put the supports inside the wall, out of sight. The wood may hold stain better than paint.

The cast cement landscaping walls are popular too. They are expensive, but easy to build. They leak dirt badly too. Have you considered just a dirt bank? They take up a lot of room and are hard to mow. You could plant an aggressive ground cover and shrubs for an attractive look. I am tired fighting my ditch out front and planted a start of English Ivy and willows.