Undergraduate research experiences are not necessarily tied to specific classes for which students register. But typically students choose to receive course credit for some of their research time.
Later (usually as a junior or a senior), once you have chosen a faculty advisor and a research topic, there are two classes for which you may choose to register:
CS 370 (Undergraduate Reading and Research): Students generally take this class during the first semester of their research activity. To be allowed to register for it, you will need to agree, with your faculty advisor, on a contract that spells out exactly what you will do and how your grade will be determined.
CS 379H (Computer Science Honors Thesis): Students generally take this course after taking CS 370. Usually (but not necessarily) the thesis is an extension of the work that was begun in CS 370. To get credit, the student must complete an Honors Thesis, which must be approved by a committee of three readers. To register for this course you must receive permission from your supervising professor and the CS department honors advisor.
For details on how to register for CS 370 or CS 379H, see your academic advisor.