Hi Viven, welcome to Steemit!

What is an upvote and how upvoting a post can benefit us and community?

Upvote is like a "like" on Facebook, but a little different. Aside from saying that you like something, you are also choosing to...

• Raise the rank of the post, so more people see it
• Raise the reward of the post, so they get money for the post!

A Steemer should accumulate more of SP , SD or Steem?

Whichever you want.

• SP = Influence, your votes are bigger!
• SD = Money, stable, you can use it to buy things without worrying about volatility
• Steem = Shares. You can buy and sell them whenever you want and they can rise or fall in value greatly

Can I post about my country and its people here or just about cryptos and things helpful to people?

It's up to you! There are 'kr' tagged posts, if you want to just boost them feel free. Or boost anything you like!

In other social platform you can promote your post using real money. What about here? :)

Yes, that is possible on Steemit too.

Can you block individuals

Yes

restrict access for your post? :)

Not yet, but soon!

Any guidelines link for this platform?

https://steemit.com/steem/@shenanigator/the-newly-updated-steemit-faq-is-now-complete