White paint, new to painting - textured wall removal ,sanding?

[annasz84]

I have to paint a property in white. I need basic advice on right preparation- I never did any painting.
2 walls in one room are textured- grainy texture that I dont like and want smooth instead .How can I do it? What tools, materials do I need. White brand of white paint do you recommend?

On top of that other walls are not smooth, there are "dents" and holes.I do not know if it's because plaster was bad or whoever painted it did a bad job. How do I make them smoother before painting? Do I need a sander?

One wall has a wallpaper. How do I remove and prepare for painting?
Thanks

Walls are painted in light grey and are not smooth.I do not know if it's because plaster was

 

[Wayners]

Last picture I can see some woodchip wallpaper.
You need to dig and see if you have plaster walls. What type of plaster? Old property with or without cavity walls?

 

[annasz84]

I dont think this is wallpaper.

 

[sparkwright]

You'll know if it's wallpaper because you should see the seams.

 

[Wayners]

Dig a bit off in a corner. Soon find if it's paper in 2 second