Is it a good practice to receive money for every service my company offer?

We have a start-up company in which we offer some educational services.

Some of our services are free to use but most of them including : online quizes, consulting and blah blah blah.

They can download tutorials, questions and some learning software for free.

Is this a good practice or it just scares everybody away and we'll be empty-handed at the end?

Wherever appropriate, virtually every company offers some items or trials for free. In general the more you can do to get people hooked on your products and services, the more likely they are to buy. Put another way, people who don't know your products and services and are unfamiliar with your company are unlikely to buy.

I have never heard of anyone being scared away by something free, unless it was defective or poor quality. Remember that people will judge you on what is free, so make sure it is as good as what you charge for.

In the case of tutorials and quizzes, this is a great opportunity for people to sample your wares before they buy. You don't state what subjects they cover, so for the sake of this question lets assume you teach people how to use computers. Pick a single topic, like how to choose a good password, and offer that as a free module. That would be sufficient for people to see how your quizzes work etc and decide if they would like to purchase the training on "how to protect yourself against viruses."

The key is to not give everything away for free, just enough to get people hooked and wanting more.

There are many real world examples of this including:

Amazon allowing you to preview sections of a book before buying.
Car dealers allowing you to take a test drive.
Paint dealers giving away color swatches.
Food manufacturers having free samples in grocery stores.
Movie trailers are free online.
Microsoft offering 90 & 180 day trials of software.

the list is endless.