I have been on this site for a year and I am still learning how to do things. To 'like' a post click on the little blue "Like" button on the lower right hand corner. On the grey line on the bottom there is a star. Click on that to give a reputation comment. Currently, you do not have any rep power but if you did whatever your power is that is how many rep points are awarded. There is a message box to write a short message and if you wish, to identify yourself.
Every 100 rep points is worth 1 rep power. Additionally, every 1000 posts is worth 1 power, and on the anniversary of each year in your membership one point is awarded. The green boxes represent rep power that is rewarded only through the rep comment process. You will get your first rep power after your first 50 posts to start with and will also become a member instead of a junior member. After 100 posts you become a senior member.
The best way to see if someone responded to your post is from someone liking it. You can click on that to take you back to the thread. Also, in your profile page click on the tab that is your name and it will list all of your post in the order that you posted them. Click on these to take you back to the thread that they were posted in and see if anyone responded to your post in another post of their own.
Likes, reputation comments, mail, friend requests, etc. will appear on the blue Notification box on the top of the page on the right-hand side. Click on this to get a detailed summary.
Glad to have you join our community. Welcome to CC.