Attack methods are able to do a variety of jobs to exploit how the target handles requests. I will give brief descriptions of each attack and what it may be used for.
This is one of the most basic methods and is on every stresser. UDP in it's simplest form just sends a bunch of information until the target cannot handle anymore.
Another basic method, UDP-LAG does the same thing as UDP but with less power causing the target to lag and not disconnect entirely.
DNS is a spoofed attack that works by tricking DNS servers into sending the target information it didn't actually request. It is often referred to as 50x because it's power amplifies normal UDP packets well above what a normal UDP attack could generate.
CHARGEN is the same concept as DNS but exploits webservers character generator and spoofs the request ip so that the target receives the information. CHARGEN is less powerful than DNS but is still very strong.
SNMP is again, another spoofed attack like DNS or CHARGEN. It sends a spoofed request to a list of servers telling them it needs information, the servers respond sending that information to the target. SNMP is stronger than DNS.
XMLRPC abuses a protocol from Wordpress sites effectively turning them into weapons by sending the target too much information.
NTP is another spoofed attack that uses the network time protocol to send bogus requests to a list of servers which then send the target its response. NTP is stronger than DNS.
ESSYN abuses the 3 way handshake of the TCP protocol causing the target to be unable to respond to legitimate requests.