I was just wondering when you get congested, no matter how many times you clear your nose by blowing it out with tissue, the boogers always come back. Where do they come from?

The lining of the nose constantly makes mucus, which protects the airways from particulate matter and small animals. When the nasal lining gets inflamed after damage or a viral infection, then the amount of mucus increases enormously.  The mucus is very protein-rich and when it dries out forms solid matter (colloquially called bogies in the UK or boogers in the US). However hard one blows one's nose that does not change the large amount of mucos being produced.