How can I access Kbin communities(magazines) and posts from Lemmy?
Do I need a separate Kbin account to post in Kbin or can I post in Kbin by using my Lemmy account?
You should be able to search them in the same format as you'd search for federated Lemmy communities. For instance, !askkbin@kbin.social should let you access Kbin's version of this community (assuming I know how to format the text correctly).
From there, you can subscribe to it from within your instance on lemmy.ml, and it'll show up in your feed as the rest of your content.