Colleges and Universities come in all shapes and sizes, and selecting the one that fits you and your goals best is extremely important. Before we get into the specific aspects of this journey please take a moment to reflect upon this statement: this choice is about you - your development personally, academically and professionally.
With that in mind let us proceed to discuss informational sessions and campus tours.
Campus tours and informational sessions are the bread and butter of getting to know a college; the former being geared towards academic programs and opportunities, the latter towards culture and social life. You can think of both as presentations a college gives to show what they have to offer. Before you attend either take time to reflect on what you want from your college experience and prepare questions that ask "does this institution offer what I want?"
Note I can give you a few examples of what to ask but at the end of the day the person who can write the best question for you is ... you, because only you know what you want. At informational sessions you can ask about majors, class sizes, faculty-student ratios and undergraduate research or internship opportunities. At campus tours ask personal questions about the general culture, student social life, how academics mesh with free time, living conditions, weather and things that matter to you.
Furthermore, keep an open eyes and ears, listen carefully and critically to what people say and what you observe on campus.
Final tip is to bring a notebook and jot down the things that are notable to you about each campus you visit or question you ask so you can remember each school when making your final decision.