The C# Selenium requires .Click(). It seems to be better suited for C#'s implementation to be uppercase, not sure why the difference though to be honest.
Also, XPATH is okay to use. CSS Selectors are supposed to be faster so try using that but I'll provide both examples for you. Another benefit of CSS Selectors is you can use * for contains where XPATH requires the exact full value, so in your case above using XPATH would require the whole href. XPath is even case sensitive in this case as well.
Shorter, faster, contains instead of equals, overall better.
By.CssSelector("a[href*='learn-c-sharp-tutorials']").Click();
*Third time's the charm... my apologies*