Logging in: a link to the login page is here.
If you cannot log in, first check that you have the correct initial password. Your initial password is the part of your Binghamton email address before the @. Note that this is not the same as the password for your Binghamton email account.
If you still cannot log in, the most common explanation is that you added the class after the date the WebWork accounts were created. In this case you should email your instructor and ask to have a WebWork account created for you. Be sure to do this from your Binghamton account.
If both of these fixes fail, please see your instructor.
About unlimited attempts for each homework problem: there is no penalty for incorrect answers. In particular, getting the answer wrong 17 times and then getting it right is just as good as getting it right the first time.
If you need to enter, say, the square root of 3, you can (in most WebWork contexts) type sqrt(3). Other mathematical functions like sine and cosine have the obvious abbreviations (sin, cos). The numbers pi and e are typed into WebWork exactly as they appear in this sentence. If this becomes a big issue I can assign everyone an working-with-WebWork problem set in which we practice these techniques. I hope to avoid this.
There is a small numerical tolerance around correct answers, so you could also write 3.14159 for pi and the answer would (usually) be correct.