Here is a Code Snippet for, if you want to know about the activities going on around your documents in a document library. For e.g. who downloaded the document or who did check in check out and at what time etc.
SPSite site = new SPSite("{YourSite}");
SPAudit _auditCol = site.Audit;
foreach (SPAuditEntry _audit in _auditCol)
{
string Loginfo = _audit.DocLocation + " – " + _audit.Event.ToString());
}