There is no easy way. It'll take time to build the knowledge, while occasionally getting ridiculed, praised, demoralized, excited etc. Just keep pushing! and best way to do that would be pick a small domain in kernel which "truly" motivates you. Try and understand each and every line of it, no matter how much time it takes. Take breaks, take detour, but keep coming back. Eventually, that one small domain will not only help you understand bigger picture, whole exercise will help in understanding other complex topics too. Remember, brain is like muscle too - it needs similar regimen of disciplined exercise to strengthen those muscles.