To try and put it simple - the Akashic Records are an energetic library (or the energetic internet, if you will) where every thing that happens in this world, incl. every action we decide to take as humans and the consequences thereof is 'recorded'...
The Akashic Records is also where our Souls Energetic Blueprint is recorded - whom we are, at our Soul self, our energetic qualities and traits, and to which we want to align/be true to, to experience a happy and fulfilling life.
We each have our own book of life (or lives), where each life we have has its own chapter.
And every time we decide and take action (or choose not to take action) that decision and the complex consequences are recorded inside the corresponding chapters in the book.
Whenever we make (or not) a decision (and act on it), we set forth specific frequencies in motion.
If our decision is not in alignment with whom we are at soul level (our soul self), we usually experience 'negative' consequences (and vice versa) - and all will be recorded in the Akashic Records.
We create our karma, and sometimes the energies from other lifetimes also carries over to the next. The same with ancestral coding, limiting beliefs, and so on.
This can be cleared energetically, when we learn how to access, read, understand and clear the records and/or those specific issues - or find someone who knows how to help us.
So the Akashic Records is a huge, extremely complex (yet simple) energetic library of events, actions and consequences in the world going all the way back to the beginning of conscious decision, that we can learn to tap into and understand why we keep experience certain things, clear old and dated coding, negative energies and influences and so on.
A clearing in the Akashic Records is often a huge aid in our Manifestation Process, and to understand why we don't initially manifest our desires right away - and to clear the way so they show up in our reality sooner rather than later.
Note that we can't clear an 'active' karma (as we simply need to change decisions and act differently to clear) but we can through the records understand the why/how a lot of our crap started in the first place, and we often carry loads of outdated energetic crap totally ready to be cleared, and where we usually feel a certain difference, sometimes even drastically, in our every day life quite quickly.
Remember - When all comes to all, YOU are the Powerful Master of Your Destiny.