Unions, associations and networks are an essential when it comes to large groups of employees. The same goes for education professionals. In Los Angeles, we had the chance to learn about UTLA which is a union for educators. So educators can be part of UTLA (as a local union) and/or part of two state (CTA and CFT) or two national (AFT and NEA) affiliates. All states have such provisions. Most countries will have a local union and a national one for sure. For more information on the union you can be part of, check with your board.
Most unions charge a certain fee for membership called dues, which will feature in your paycheck as a deduction if you become a member. The dues are very nominal and are mostly used for keeping the affiliations and organizing the members. There could be varying levels of membership and participation in a union with which you can avail of various legal, administrative and training opportunities, not to mention discounts and free entertainment. Some throw in insurance and loans too.
As far as issues, voting and representation goes, the union depends on a House of Representatives, Boards, Committees and of course the active members. UTLA has 47000 members of which some are not active.
Membership is not dependent on active participation, although it is encouraged. Participation in numbers is important in having a successful union though and thus active members can hope to become presidents or occupy posts of authority.
The union may take a particular stand on an issue that all the members may not agree with, but good unions welcome differing opinions. However, any final authorization votes (such as for a strike or a contract agreement) would need an approval of a majority of the voting members. And if it is not an issue that can be solved by voting alone, the various committees help guide the actions of the union.