This is the preferred method for linking videos to your posts. YouTube is preferred over Google Drive, so if you have a choice, that is the preference, but do not be deterred if you only have Google Drive, that is also acceptable.

YouTube: Make sure your setting is to have it be able to be viewed by those with the link.

Click the "Share" option, Copy Link.

Go to the forum, in the forum text box you where want your video to appear, paste the link where you want it to appear in the box. If you want text above it, type in the text, use the space bar to add a space and paste the link, or use the return key and paste it on the next line. 

Alternatively, you can add your text, then a space or return. Up in the menu bar above the text box is a link, click the link, paste the URL to the top rectangle. Below the top rectangle, you can type text that you want displayed for the link. It is automatically filled in with the link address. You can delete that and type in something more descriptive, if you want, ie the title of the song. Click OK. Instead of the YouTube screens appearing in your post, the text you chose to display will be shown.

Google Drive would be done pretty much the same way. I do not do Google Drive for the videos here, but you need to make sure that those who have the link can view. I think there is a place you click to get the share options. Choose to copy the link. The rest is just as stated above for pasting it into your post.