You needed good grades to get into college and good grades to get into medical school--getting into residency is no different. Grades in the first two years are important, but residency directors care much more about clinical clerkship performance. Strong grades in Core Surgery and Core Medicine clerkships are very desirable. A high grade in your Urology sub-intership(s) is extremely helpful. Beyond these specific clerkships, it is your overall pattern of grades that will stand out. What's most coveted, not surprisingly, is AOA, as this gives the residency admission committee the best evidence that you are among the top of your class. You can absolutely still match without being AOA, but it will be more difficult to match at top programs. Some top medical schools do not have AOA chapters, and ERAS allows you to select "No AOA Chapter At My School" option on the application. Bottom line: if you think your grades are marginal, you should find a good advisor to council you on where you stand.
Board scores are extremely important. They provide the most objective comparison of applicants and play a significant role in the selection of candidates for interviews. You will find that once you have made it to the interview round, these scores begin to carry significantly less weight. Here is a rough breakdown of scores:
< 215 - seek advice on whether you have a reasonable chance at matching; people do match with these scores, but only with a very solid application.
215-230 - your score may hurt you in the eyes of many programs, but many people match every year with these scores.
230-240 - these are solid scores and you should certainly do fine. If you are aiming for top-tier programs, however, this is hopefully not the strongest part of your application.
240-250 - you are in great shape.
>250 - your board score is outstanding and will stand out.
Having USMLE Step 2 on your application is not at all necessary, but if you believe that your score on Step 1 is marginal, doing well on Step 2 can be a very strong move. The best advice is to take Step 2 after you submitted your ERAS application and all the schools have downloaded your USMLE score report (early November is perfect). Be sure that you do NOT select "automatic score reporting" when filling out the application. This way, if your Step 2 scores are high, you can instruct ERAS to release them to the residency programs in time to help you. If you do no better on Step 2 than on Step 1, do not release your scores and no one finds out. Every year we see applicants who apply with excellent Step 1 scores and poor Step 2 scores--these students have completely unnecessarily severely damaged their application. Note, recently the UCSF program (see details) has announced a requirement that students must have Step 2 scores submitted prior to being ranked.