You can't figure out whether your furniture will fit until you know the size of your space. But most of us have no room in the budget for design software after buying all that furniture! So do your layout the easy, simple way: take a tape measure and measure each wall of your room, the size of the windows and doors, and take note whether the doors open out or in.
You will draw your room on graph paper. Each 1/4 inch square will equal 1 foot. It doesn't have to be fancy, but it might appear neater and easier for others to read if you use a ruler or straight-edge.