G-31, it would seem from your further line of questions that you have skipped the entire "introduction and basic reloading" section of the reloading manual that you (hopefully) have read. If I'm correct, I'll be the first to bust your cohonas and advise you to go do some reading. If I am wrong, my apologies.
The "rocket shaped think" is a chamfering/deburring tool used to "dress" the case mouth. One end puts a slight angle on the inside of the case mouth to assist in starting a bullet, and the other end will deburr the outside of the case mouth to remove any rough edges left after trimming the case to proper length. Case trimming is not required for straight wall cases. Your 357SIG is a bottlenecked case and trimming may be required to keep the cases at or under SAAMI cartridge specifications.
A micrometer is a caliper, either digital or dial. These are used for measuring your COL which cannot be done accurately by simply comparing to factory rounds. Get one - digital calipers can be had at Harbor Freight on sale for around $10.
There are a bunch of VERY knowledgable reloaders here on this board who enjoy helping others to learn the art of reloading. It is preferred that newbies, at a minimum, do some of their own homework by reading about reloading.