Acrylic paints can be mixed with water and applied to many different surfaces including paper, wood or canvas. For an exercise in creating white values from paper, you might consider painting the pine tree on Bristol board or watercolour paper. When mixed with water, acrylic paint handles much like watercolour except that once the medium dries, it remains hard and will not mix with a second application of paint.
Draw pine trees with a pencil in your sketchbook. Erase whatever you don't like. Or you can always turn to a new page and start another sketch.
Draw the main trunk as a round cylinder and the bunches of needles as one three-dimensional mass.
Draw a few close-up sketches of the branches or pine cones.
Make several detailed sketches until drawing the tree seems natural.
Make the preliminary sketch on watercolour paper or Bristol board with the pencil. Use the eraser as needed. Let the tree take up most of the space on the paper without worrying about detail.
Wet the tree areas with clear water and then fill in the trunk and branches with a mixture of burnt umber and burnt sierra. Mix the paint with ample amounts of water.
Wet the foliage area and fill these areas with sap green. You can mix the sap green with a little yellow ochre if you like.
Do a quick coverage of the foreground with a wet wash. Try and match the colour of the foreground with whatever paint you have.
Repeat for the background forest area.
Wet the sky area with a wide brush. If the weather is cloudy or hazy you can use dirty water to prep the area. Add a wet wash of cerulean blue. Use clear blue cerulean, if the skies are cloudless, or a blue mixture if skies are hazy.
Add details to all areas of the painting except the sky.
Keep your wash water as clean as possible.
Don't try to rub out (or scrape off) areas that you don't like. While sometimes successful with true watercolours, this technique probably won't work with acrylic paints. Many types of paper are available for use by the artist. Finding the right paper for your needs requires some trial and error and experimentation. Bristol board is a stiff kind of paper that absorbs less water than watercolour paper.