I notice you ask some very basic questions, its okay though I highly recommend you grab some SEO books (Google, its a ton) or basic tutorials to learn the fundamentals of SEO before you do serious moves. Just do it!
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Answer your questions:
1, blog comment sections in most cases, all no-follow links, yes, you can comment on some niche-related blogs in order to diversify your links profile. (to make your backlinks more natural) If you spam hell lot of it, for example, 100,000 comments links to your money site, do you think its natural?
2, content syndicating, so you typed "syndicate" right? It simply means, spread your same content to multiple platforms, result as duplicate contents all over the internet (maybe videos) , while Guest blog post is, you post some high quality articles on other people's website, which is very good white hat move, these days.
Learn basic first, good luck.