How should I ask my advisor on help with something I should know how to do? I am creating a mathematical model in R (programming language) as part of my thesis. I created the first part of the model no problem and sent it to my advisor. She said I did a fantastic job on it. For the second part, I need to look over some class notes as we did it in class last year. This part is very challenging and I even remember in class that I didn't fully understand it. I have been working for 3 days trying to create this model, but I am not even close. I just can't figure out the code to use. I am trying to use the same code as we did in class, but my model is quite a bit different than the class examples so I can't figure it out. I tried looking online as well, but this type of model analysis is not very common so there are not many resources available. 

I need to get going on the project so it may be better to meet with my advisor so she can show me how to do it. But I am afraid to ask as this is something I should know how to do. I would like your help with drafting up an email to ask her for help.
The way to frame your question can have a huge impact. If you did your due diligence and researched some material on this (books, lectures, papers, StackExchange!), and are still stuck, then there is a chance that your questions are more than valid.

If you start your email or personal question by: "I have tried three ways to do this.."  and then show/tell them that you have honestly tried your best, your supervisor should help you out. That's what they are for.

Also, feeling like a fool today may accelerate your advance in the future. Postponing communication like this is not always wise (given that you've done your part).