Different fabrics leave some floss while sewing the project, which can pile up and cause blockage in your machine. Sometimes the fabric of your project, that you are sewing, can get stuck into the dog feed of your machine that causes jamming. With my personal experience, this is one of the most common factors of machine jamming. To clear this, you should not force it out.
Firstly, lift the presser foot of your machine that is holding the fabric of your project. Then remove the needle so that you will not get hurt in the process. Then slowly pull the fabric out. This will require lifting the fabric enough to snip at the threads and then pull the fabric free of the machine.
If some pieces of the fabric are left on the dog feed, clean them. Also, check your sewing machine needle, if it is bent then replace it with a new one and, if it is not then you are good to go. Even a slightly bent needle can cause a thread jam and can even break. Your machine would work smoothly.