The match shows how well someone fits an opportunity. It has three parts that count equally: the role, the skills, and the certificates.
For the skills you set the weight. A skill weighted as essential counts ten times as much as nice to have, important counts three times. This is how you decide what matters most for an opportunity.
Related skills count too. Someone with a related or more specialised skill earns partial points, even without the exact one required. So nobody drops out just because a skill is named differently.

A low match usually means a skill marked as essential or a required certificate is missing. You can still apply and explain in your message why you fit.
Which information does the match use?
The match compares an opportunity with the profile of each person. It only uses the three parts named above: the role, the skills and the certificates that the opportunity asks for. No other information from the profile counts towards the match.
Personal details such as gender or age are not part of the match.
From which match do I appear as a suggestion?
For each opportunity, the responsible person sees a list of people whose profile fits. By default, this list only shows people with a match of 70% or more. The responsible person can move this threshold anywhere between 0 and 100%.
The threshold only filters that list. Your own view works differently: every opportunity shows your match, and you can always apply, whatever your match is.
Why do I not show up for an opportunity that fits me?
Your match may be below the threshold that the responsible person has set for the list.
Or none of your skills has a current level yet. As long as no skill on your profile has a current level, no match is calculated for you.