title: sharepoint website modification and user activity interception
body: <p>There are several topics I have questions about, where googling did no good to me, neither did it lead me to any valuable resources.</p>
  <ol>
  <li>Can I modify the SharePoint page to my needs, like can I customize it so much that I can add something like a 'calculator of services'(like there are dropdowns and depending on different selected ones calculated results change)on it. I saw that I can embed html, but everything I saw and stumbled up-on is kind of abstract.</li>
  <li>Can I intercept the users who e.g.: click on a button. I have a SharePoint webpage with users within it, if user1 clicked a button can I be informed about that or can I trigger some actions as a result ?</li>
  <li>Can I have a file upload on SharePoint page ?</li>
  </ol>
  <p>Any resource/comment/friendly advice will be valuable for me.</p>
  <p>Thanks.</p>