You are able to form a magic seed that will grow into a Nascent Mana Core, the additional core then will grow at an increased rate until it catches up to your main core. In addition to this increased rate of passive growth, the effects of practice and rituals are multiplied by your total number of cores. Once your new core has caught up to your main core, you may link your cores together allowing all linked cores to share the same amount of growth across one another.
Each additional core allows you another 'instance' of casting, multiplicatively increasing the number of spells you can cast simultaneously. You can cast spells and grant rituals that require multiple people on your own by using linked cores as a fill-in for another person.
Once you have linked the newest core you may begin to form another seed. Each additional core linked increases your Mana Concentration, allowing you to get more Magic out of a smaller quantity of Mana. Linked cores also increase your total Mana throughput, allowing you to cast both a higher quality and quantity of spells at once. You may repeat this process infinitely as there is no limit to the number of cores you can have.
Once you have linked your third core, you may begin to permanently designate cores as specialized, allowing them to perform a specific branch of magic at a much higher level than a regular core. The specialization can be something as broad as Conjuration, or something as niche as Repair of Small Objects, though the broader it is, the lesser the boost it provides. Each specialized core forms a unique ability fit for whichever has been selected. It is up to you to form your own path beyond this step. Nothing is off-limits for you in regards to magic, only time will be able to stop you, and not for much longer.