A friend of mine said that opening a web blog could help me to find a job.
Is it true ? Or what should I write any way ?
I afaid that If I will write specific techinal things, know-hows, etc.., people will stole those information and credit.
What you think ?
Think it through.
Consider first the balance in the potential audience for your writings between people who will want to steal and take credit for what you publish, and those who won't. Consider too that 1) people get "credit" for finding and sharing good information while providing attribution. 2) The easiest way to share information on the web is to link to the existing page. Its not just Facebook and twitter either. Most blogging software has an easy way to click a bookmarklet to create a new blog post that excerpts and links to the original web page.
Consider too that for someone to steal from your writings, they first have to find your writings. If they can find your writings, then other people can. Your biggest problem is likely to be that no one pays any attention, there are ways around that. In fact, just putting a link in your signature on forums you participate on can make a noticeable impact. The better you are at getting attention to your writings, the more likely it is that your writings will appear higher in search listings that that of people who try ripping you off.
Finally, consider that the most important audience for your work is probably potential employers. How are they going to find out about your work? Perhaps they'll discover you on their own, but more likely is that they'll find out about you by another means, by someone forwarding them your resume, or you applying for a job. They'll check out your blog because they want a quick way of getting a better sense of you. If they like the first thing they read, they may read more. If your posts make a favorable impression then maybe they'll do a search to see if there is any doubt about the original origin of the writing on your blog. If they care enough to do that, and they discover copies of your writing, there is probably a good chance that they'll be able to figure out that you are indeed the original source.
Now, all of this ignores the question of whether starting a blog is a good use of your time when it comes to searching for a job. I can't really answer that. I'd guess that there are probably lower hanging fruit, easier/quicker things you can do. However, if you find yourself with a lot of time on your hands and fill it by things like constantly checking for new posts on EEVBlog/forums, writing blog posts probably isn't a bad use of your time. Writing something down forces you to clarify your thinking, if only for yourself. Doing so also makes it easier to communicate your thinking to others, and that is itself valuable in getting and doing most jobs that require thought and expertise.
If you start a blog and do get a job, consider keeping the blog up, because it could make it easier to find the next job too. My wife hasn't found a job because of her blog, and she hasn't updated it in 18 months, but people are still finding and reading the articles she wrote (and the google ads on them still make a little money every month). My old posts on my various blogs still find readers too.