User-agent: *
Disallow:

The first line of code "User-agent" means the search engine bots, which means the software that Google and other search engines will send to your website to crawl it and then index it

Putting the * , the star sign means all Search Engine bots are welcome.

I like letting the first line intact, because i like all Search Engines to come and index my website.

Now, the second line of code means whether you want to allow the Search Engine bots or not to see your website.

For example, by putting this line of code (below), you are telling all the Search Engines NOT to index your site:

Disallow: /

Many people who have private family websites and blogs tend to use this line of code in the robots.txt file.

As an example, for webpages you want search engines NOT to index, put this line of code:

User-agent: *
Disallow: /your-bonuses/
Disallow: /my-free-report/