Being in a union generally means more bargaining power and security for you as an employee. Having a representative will mean you are better protected, and that you have somebody to speak for you. Also, they are generally very knowledgeable about worker's rights that the average person which will help you.
They typically have higher pay rates and often have stronger benefit plans. However, they also charge dues for membership, and if they strike, you may be forced to be unemployed whether you want to work or not.
Your going to have a large group of people supporting your career choice in your trade. They will be there for contract negotiations regarding pay/wages/schedules, etc. Beware though, you also have restrictions imposed on your as well (such as if no work available, they keep you from freelancing on your own).
The advantages will vary based on the trade or profession that the union represents. Generally, unions will provide a guaranteed rate of pay and wage increases, legal help with grievances against employers, and protection of benefits such as vacation time, sick leave, and insurance.
The advantage of being in a union is that u are able to serve the nation. the union u join should have experienced persons who are able to cooperate you.
Union is strength. There are many proverbs over this topic. When we join we can get more knowledge and all the things we need. It will be strength for us when we all join together.