I already answered part of the question (what witnesses do) in a reply to another user's comment on this post. You can find that info there.
As far as becoming a witness, witnesses get paid per block they produce. Here is a guide to get you started if interested: https://steemit.com/witness-category/@timcliff/steps-for-setting-up-a-witness-node-the-manual-way. You should be aware though, that getting enough votes to run a "profitable" witness can be quite difficult. Many witnesses have to run their servers at a loss for quite some time before they can prove to the community/stakeholders that they are a valuable and trustworthy witness.
If I just create blocks but didn't get upvote will I still receive SP in reward I only want to do that for the sake of SP?
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You do not get any blocks to produce if you don’t have any votes.
Ohhh I see are these votes I get on my blogs and comments am I right?
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No, they are unrelated.
Witness votes are done here: https://steemit.com/~witnesses
Ohhh that is difficult for me at the moment than thanks for your kind information otherwise I might have invest some money and than find out it is not possible in amount of time I have.
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