While blenders and food processors serve similar purposes, they are often used in very different ways. It is a good idea to have one of each in your kitchen, but if this is not possible, they can be used almost interchangeably in your kitchen for several different tasks. If you only have a blender, you can perform many cooking tasks that some might use a food processor for. While their function is very similar, you may need to adjust the way you use a blender if you are trying to achieve an effect that is more like a food processor.
Slow down the blending process. Blenders typically work at a higher speed than most food processors, which might leave whatever you are trying to create much smoother than you want it to be. To simulate the power of a food processor, push and release the buttons repeatedly, as opposed to pressing the buttons for an extended amount of time.
Avoid the "liquefy" and "puree" settings on your blender, unless that is the result you are attempting to create. Blenders are typically used for making liquid drinks, chopping ice, or pureeing soups, whereas food processors are mainly used to chop and combine.
Use less liquid in your blender than what your recipe calls for, at least initially. This will help you replicate the effect of using a food processor without over-liquefying your food. As you are blending, you can always add more liquid for a smoother, more combined result.
Do not try to use the blender to shred, grate, or slice food. While a food processor has a number of different attachments that can achieve variations in cutting size, the blender offers only one cutting tool that is capable of coarsely chopping or blending. If you do not have a food processor, you will need to shred, grate, or slice by hand with a knife.