Starting and viewing a search does not cost credits. Credits are only used for paid actions, such as requesting contact details through Find e-mail & phonenumber or other features in your environment that are credit-based. It is also possible to evaluate larger numbers of profiles at once against your criteria in a search. In that case, you can choose the volume yourself, after which the shown number of credits will be deducted.
What to look for
If an action costs credits, you see that in the interface before you continue. That lets you decide whether you want to proceed.
Practical use
Feel free to use searches to review and refine candidates. Only request contact details or other credit-based actions when you really want to follow up on a candidate.