Validation can help in different ways depending on your situation.
If you have the certificate or diploma that enables you to enter higher education in your own country, you may not need validation.  In the European Union all countries have national agencies NARIC which help universities to understand and verify diplomas issued in other countries, and there is someone in each university who has this responsibility.
If you did not complete your studies, were not able to take the examinations, or if you have lost your diploma or it has been destroyed, or if it cannot be verified because of conflict, political or economic crisis in home country, then validation may be able to help you because it offers an alternative way to demonstrate what you know, understand and can do without having to start at the beginning again.
If you have not followed a formal curriculum in a classroom setting that leads to the usual entry qualifications, then validation is particularly useful to you because it can take account of other forms of learning.
If you have participated in short courses, organised study visits, work placements, work-based learning, skills training that did not lead to a certificate or diploma but were important in your personal and professional development, validation can help you get recognition for this ‘non-formal learning’.
If you have been in paid or unpaid work, taken part in voluntary activities (for example in trade unions or NGOs) or you have an individual interest that you have pursued (anything from motor mechanics to ancient history) then you have learned from those experiences and validation can help you get recognition for this ‘informal learning’.
In practice, you may have a mixture of these things, for example, some certificates but not enough or not quite the right ones, some work-based training, some special individual interest.  Validation can help you to bring all this learning together, to review it and demonstrate it.  You can then compare this to the formal curriculum of higher education study that you wish to enter.
So validation can help you to enter a specific course or programme of studies.  In some cases, it can also enable you to obtain credits for part of the formal course of study (cross ref to Guidelines explaining credits in HE) so that you do not have to follow the whole programme but can take a shortened version to obtain the full diploma more quickly.  And in some cases it may be possible to obtain the whole diploma in this way.