-ic, or -ical, is a suffix that means to have the character of something. Examples are psychological (involving psyche), methodical (something done with an established procedure), or majestic (showing majesty, dignity.)
-ion is a suffix that implies action or condition, such as union (like unity, where uni is 'one') or creation (an act of creating, or making something.)
-ist usually describes someone or something that performs a specific action. (A scientist does science and a geologist studies geology.)
-ive is a suffix that describes something's nature (something that's informative informs you or gives information, and someone that's inquisitive inquires, or asks questions.)
-ment is a suffix that, like -ion, describes conditions. (For example, development, which is the process of developing, or management.)
-ous is a suffix that shows what something is characterized by (like jealous, religious, or ridiculous.)
There are a lot of resources for studying suffixes and prefixes and their meanings, as well as roots.
