Mathematicians gather at conferences to discuss and share their research. Conferences range in size and scope. Some conferences are small and focus on a specific subdiscipline. Others are large and cover a broad range of topics. Here are some ways in which undergraduates benefit from attending conferences:
Giving talks or presenting a posters on undergraduate research
Building relationships with and joining communities of mathematicians, both personal and professional
Becoming acquainted with modern developments and fashion in mathematical research, both on a broad scale and in individual subdisciplines
Here are some additional things to note:
Conferences often offer funding (to cover food/housing/travel expenses) specifically for undergraduates. Some funding opportunities require an application.
Attending a conference, in addition to presenting undergraduate research, can be put on a CV.
To learn more about conferences and which ones might be fitting for you to attend, ask your peers and faculty mentors!