I agree with the recommendation to ask for the report in advance. I don't think they have to provide it in advance and might not have it ready, but it can't hurt to ask. In any case, the only things you'll sign at the meeting are things like a "notice of procedural safeguards," acknowledgment that they provided you with certain documents required by law, and an attendance sheet that confirms you were there.
Bring a notebook or note pad, a folder to store all of the papers you receive, and a pen. Take lots of notes, ask lots of questions to make sure that you understand the reports.
They probably did some assessments of various intelligence measures as well as subject-level aptitude tests. The most common general intelligence test is known as the WISC (probably version five although some are still using version 4). Version 4 measures verbal reasoning, perceptual reasoning, working memory and processing speed while version 5 breaks one of those out into two separate sections. Each of those areas will have sub-tests. Each test will have a raw score and a scaled score. A score of 100 is average and they will explain the ranges of each score. What they're looking for is overall "IQ" (an average of all of the 4 or 5 areas) and more importantly, variances across each test. These variances can help shed some light on various learning disabilities or challenges. For example, my 6th grader was just tested and everything except processing speed was in a high average or higher range while processing speed was very, very low. This is a sign of specific learning patterns, prompted other testing, and indicates what types of support will help him. The subject tests will tell you at what grade level your child is performing in one area vs another, so you can see and quantify relatives strengths and weaknesses and build on those strengths and support the weaknesses.
The testing may also have included some basic measures of attentiveness, visual processing, markers of anxiety or mood issues and other measures. Some common tests for these are the Conner's scales (you may have been asked to fill out a booklet of questions) and a test called the Bender Gestalt.
These meetings usually start with an update from the classroom teacher on your child's performance and his or her observations about your child. Then the psychologist usually goes through a report that contains the testing results. This part can be confusing and overwhelming, even if you're familiar with the tests. Sometimes seeing your child's struggles laid out in black and white on a page can be emotional. Low scores are good because they confirm the struggle and give your child access to the supports that they need, but it can be hard to have your suspicions confirmed so don't be embarrassed or surprised if you tear up a bit when you first read the report. It's totally normal and the folks in the room with you will understand. They will then go through what they recommend for accommodations, if any, and perhaps will recommend that you seek further testing outside of school. If a disability is confirmed by testing and they put together an accommodation plan, they will go over their suggestions with you. You can make any comments or corrections right there that they will incorporate into a version that they mail to you. You then have a certain period of time to accept the plan as-is, reject all or parts of it, or ask for additional accommodations or measures to be recorded. If you have a friend who has experience in this area, it can be helpful to run this by someone else you know and trust to see if they have any other suggestions. Then you sign it and send it back and any accommodations or services will begin.
Hopefully this was helpful to you - it's great to have the testing done and be able to move forward with a plan to help your child!