Actually there is kind of major difference between Germany and the rest of the EU.
In Germany, basically every company above a certain size (say 7 or 18 employees or so) can or must must have worker's council (the first size-level is for "can" and the second is for "must-have", but I'm not sure about the size anymore as it changes from time to time). This is the starting point.
For most of the industries, there is also one or more specific unions.
Also, for all large corporations, there needs to be a Supervisory Board (similar to Board of Directors in the USA), of which 50% must be filled-in by worker's council members or unions. In larger companies, there can be dedicated worker's council members, who are paid by the employer but do only worker's council work.
Also, in Germany, there is no such thing as an "HR-Department". There is a "Personalabteilung" (Personnel-Department), that actually represents the employer's interest and there is the worker's council that represents the employee's interest. Therefore, there is also no interest-of-conflict within those organizations such as in a hybrid HR-department.
Lastly, membership in a Union is purely voluntary, i.e. you can work for a corporation/company that is member of a Employer's Organization but that doesn't necessarily require you to be member of a Union.
If the Employer (the company) is member of a specific collective-bargaining Employer's Organization, the salaries of all (or nearly all) rank-and-file employees is agreed-upon between the Union and the Employer's Organization. Technically, this also means that once the company leaves the Employer's-Organization, they do not need to abide by the rules of Collective Bargaining, meaning that they can either negotiate directly with the Unions or directly with each employee separately.
Usually, most companies (apart from the small ones) are members of such Employer's Organizations as that makes it really easy doing the yearly salary-negotiation-dance (as I call it). But unless you are a member, you do not need to, but you still can abide by the rules of Collective Bargaining in your industry.
For example: If you are a software company, you can abide by the rules of Collective Bargaining between Verdi (Services Union) and the Services Employer's Organization (or something like that) or you can negotiate directly with the Union or you can negotiate directly with each employee or group-of-employees directly (if you are not a member of such an organization). But if you are member of, let's say, the "Software Engineers' Service Employer Org" (just to make up an org) and they agreed to Collectively Bargain with Verdi, you must implement their agreement or leave the Org.
The employees who become members of Unions must pay a monthly fee to the Union (a small fraction of their salary). In exchange, they have the right to strike and be paid some amount during such a strike by the Union (I don't know all the details). The counter-tool the employers have against striking employees is "Lock Out", i.e. the employers can "strike" as well by locking out employees, in which case the Unions must pay the employees some part of their salaries.
Germany is extremely consensus-driven in this regard and usually you won't see strikes like in France. Since there is worker's council and/or supervisory-board membership, the worker's council-members as well as the employee-representations in the Supervisory Board have an equal interest in keeping the company healthy as well as achieving good terms for employees. The worker's council-members are elected (once a year, or once every two years, I don't know) by the employees, so they have an interest not only to make sure that the company is healthy but also that the employees are happy as well...
Rest of Europe is quite different insofar as they don't have these rules in this detail, and most of them don't have the Supervisory Board-Requirements...
Hope this helps.