dynamic vs. static

Hello, I have a couple of questions regarding PHP setup. I have succesfully installed dynamic PHP and it works, and everything is great. I have just found out about TWIG and want to try it, so now i am faced with installing static PHP. It will not configure now because it says that it cannot find the httpd.h file in the directory i give it, which is /usr/include/apache even though /usr/include/apache/httpd.h does exist! question 1: What is the difference between my dynamic installation of PHP and this new static install? And, will this have an effect on my current installation? question 2: Why does it not find my httpd.h file, even though it is physically there? question 3: I look for php-imap and cannot find it, yet, in my /usr/lib/apache directory i do find mod_imap.so... i suppose i still need this thing called php-imap ? I did look through the documentation about dynamic vs. static, but could not find a clear explanation. thanks in advance!