Details will vary country-to-country, even within EU member states.
Here's the break-down:
That's the headline 'salary' figure. It's what you'd apparently receive in cash if the Government opted out of income-related taxes.
These are specific, itemised deductions, where you are contributing to the common pot for something. This can include income taxes paid at source, healthcare, social security and pension contributions and the like. Some of these may explicitly create benefits for you that can be accessed at a later date. And some you may be able to choose options for or even opt out of.
You may have other compulsory or optional deductions controlled by the employer. These may overlap statutory deductions - for instance, you may be able to choose between (or blend) state, employer-specified or personal pension plans, health cover and the like.
You may be entitled to non-cash benefits that the tax authorities deem to have a financial value. And these can increase the tax you pay. Again, some of this may be optional or somewhat controllable. For instance, in some countries if your employer wants to provide a cellphone you may be taxed in obscure and punitive ways, which you could avoid by using your own phone and expensing business usage. If you're entitled to use of leisure facilities, and the employer has agreed the arrangement with the tax authorities, you may not be able to avoid the additional tax even if you never use the service.
All of the above relates to you as an individual employee. The employer may in addition be taxed invisibly from your point of view. That doesn't directly affect your earnings or tax position, but it does increase the cost of employing you. In a startup context, you could regard that as a reduction in your earnings.
In the example you quote, that's what's going on. So for instance, in the UK, employees pay National Insurance contributions - this is deducted by the employer, visible on a payslip and forms part of the individual's lifetime contribution record (relevant to the eligibility for and calculation of the state pension). And in addition, employers pay further National Insurance contributions, which result from your employment but are not in any sense your contributions.
The point isn't that this element is 'already included' - it's just how the system is constructed overall. And - naturally! - the composition and overall effect varies significantly from country to country.