Here's how to draw a basic cube:
Materials:

Pencil

Eraser

Ruler (optional)

Paper
Steps:

Draw a square: Lightly sketch a square in the center of your paper. This will be the front face of your cube. You can use a ruler to make sure the sides are straight, or eyeball it for a more freehand look.

Add a diagonal line: Draw a diagonal line from the top left corner of the square to the bottom right corner. This line will help you visualize the depth of the cube.

Extend the sides: From the top right corner of the square, draw a line extending upwards at an angle away from the diagonal line you just drew. This line should be about the same length as the side of the square.

Extend the top line: From the end of the line you just drew in step 3, draw a horizontal line to the left until it meets the left side of the original square. This creates the top face of the cube.

Complete the box: From the bottom right corner of the original square, draw a line parallel to the line you drew in step 3. This line should go down and to the left, meeting the bottom line of the original square a bit past the halfway point. This creates the bottom side of the cube.

Add back lines: From the endpoint of the line you just drew in step 5 (a bit past the halfway point of the bottom line of the square), draw another diagonal line upwards towards the left, meeting the diagonal line you drew in step 2. This creates the back side of the cube.

Erase unnecessary lines: Once you have all the main lines of the cube drawn, erase the diagonal line going through the front face of the cube (the one you drew in step 2) and any other stray lines you don't want.

Outline and details (optional): Now that you have the basic cube shape, you can darken the visible edges and add details like shading or highlights to make it look more 3D. You can also add lines to represent the individual faces of the cube.
Here are some additional tips:

Use light pencil strokes at first so you can easily erase mistakes.

You can practice drawing squares and diagonal lines on a separate piece of paper before starting on your cube.

There are different ways to shade a cube to create a 3D effect. You can find tutorials online or in art books for shading techniques.