A trip to the lumber yard is always a day well spent. While there, you can get just about any type of wood you need, cut to whatever size you need. It is always a good idea to go there with a plan. You want to know what type of wood you are buying and how much. This will allow you to avoid making mistakes, paying too much and making unnecessary trips.
In the case of interior wall framing, there are some important considerations. You should know if the wall you are working on is a load bearing wall. This is a wall that is holding something else up, usually either another wall or part of the ceiling or floor. Taking down this wall without making modifications could result in property damage and even injury.
Once you have identified the wall you will be framing, it is good to know the basics. Most framed walls are built from 2 x 4 framing lumber. This can easily be obtained from the lumber yard. From there, it is just a matter of knowing how much you need and then measuring. An interior framing wall will require a bottom plate and a top plate. The size of the room will determine how many feet of 2 x 4s are needed.
You will also need to know the height of the room, as you will need wood that goes from the floor to the ceiling. Most walls will require the vertical placing of wood every sixteen inches. So, you would need to know how long the room is, and how high, and do the arithmetic to come up with the amount of wood needed.
Once at the lumber yard, you can tell the personnel the exact measurements of the wood you want. When you get home, you will have to make some cuts to make the pieces fit, but you should have everything you need.