Bubble diagrams are a useful tool in the beginning stages of designing your home. Before you can begin defining the spaces with walls on the floor plan, you need to understand the relationships between the spaces as you picture them in your mind.
Architects begin with a bubble diagram. The Bubbles represent interior spaces and their importance and relationship to each other. You can do simple ones with your Open Office Draw tool (free download) or the Microsoft Paint program on your Windows computer. These will be easier to change and manipulate, but you can do them with plain old pencil and paper also.
Larger bubbles mean larger rooms, overlapping bubbles are spaces that are accessible from another space. You can also let every bubble float free and draw connecting lines to indicate access and flow. As you plan the spaces with bubbles, you will begin to get a better feel for the spaces you want and how they should relate. It is easier to do this with the abstract tool of a bubble rather that try to sit down and begin defining spaces with walls and the technical relationships between rooms, access and flow. This exercise will save you time and money later if you are drafting your own plans or paying a designer to do them. You will also see errors in your judgement by conceptualizing what was a thought into concrete relationship on paper. This process is critical and precedes formal space-planning and is reiterative ( it is cheaper to make mistakes here) but it will help you clarify how you want the space to relate and flow and will be very helpful when floor plans are drawn.
Go ahead, have fun and draw away.