Go to your steam library and go the search bar. At the search bar, type "Half-Life". If nothing shows up, you may not own the game. You MUST own the game to play it. When you see the game called "Half-Life" click start. If it says "Install" then that means the game is not installed. You MUST have the game installed to play it.

When the game is open, press L. Shift and Tab at the same time. A menu should appear. Go to the bottom and click the browser button. It looks almost like the Apple safari browser. When the browser is open, go to the search bar and type "youtube.com". Once the page has loaded, go to the YouTube search bar and type "Half Life 1 walkthrough". Click on the video that is a walkthrough for Half-Life.
There is a walkthrough I found that works in this this guide.

Press L. Shift and Tab at the same time. In the actual game now, click "New Game" then select "Play Half-Life". Now you should be playing the game. When you get confused go to the guide by pressing L. Shift and Tab at the same time, go to where you are in the game, and copy what the guide does.

You can now play Half-Life without getting stuck!!!