Just sit down and start chewing on it.
Don't think: I should finish this within X days/weeks/years.
Read it sentence by sentence, pausing whenever you encounter anything you do not understand, and then apply all means at your disposal to understand it (including asking others). Do not set any time limits for this, but don't give up on it either, but whenever you are stuck and wrestling with something say to yourself: this is precisely why I have embarked on this enterprise. It is only when we are stuck that we have a real opportunity to learn something.