I guess you would have already introduced yourself in a Japanese speaking community in Facebook or other social media by now.
Now, the most easiest way to communicate with Japanese people is showing your sympathy, expressing approval or agreeing with somebody else. It's much easier than arguing something you can't agree, or explaining something they don't know. So, if you are not so confident in your Japanese level, start with these activity.
いいですね IidesuneThe most common expression for this purpose is "いいですね"(iidesune) which means simply "It is good.". You can reply with this expression to all the posts instead of tapping on "like" button in Facebook.
"It's not raining today."
"I ate a hamburger."
"I like Shinkai Makoto."
"desu" as in "Iidesune!" makes a sentence polite, so if you reply to your close friend or kids, just "いいね！"（Iine!）will be enough.
When somebody posted his or her opinion, "Iidesune!" is not wrong, but "Doukan desu." is more appropriate.
(Tedukawa Miyazakiya Shinkaiyorimo idaina sakkada.)
"Tezuka was a greater creator than Miyazaki or Shinkai."
As I wrote above, "desu" as in "Doukan desu" is a polite way. So when you speak with your close friends, you can omit "desu".
"I want to watch the movie "Your name"."
However, when there is no opinion in a post, you can not use this expression.
"I watched the movie "Your name."."
"Doukan desu." (Wrong)
たいへんですね。 Taihen desune.
"Iidesune" means "It is good.", as I wrote above, so apparently, you can not use this expression when you show your sympathy to a person who experienced something bad, such as losing their money, or catching a cold.
In that case, you can say 「たいへんですね」(Taihen desune) or "That is hard." literally.
「頭が痛い」(Atamaga itai) "I have a headache."
「お金がない」(Okanega nai) "I have no money."
「休みがほしい」(Yasumiga hoshii) "I want a day off." (I don't have day off.)
Cultural NoteIn Japan, evaluating directly somebody who is superior is not considered polite.
For example, "You are a good teacher." is not recommendable even though it is a positive evaluation.
In this case, you can say "勉強になりました"(Benkyouni narimasita) or "I could learn a lot (from your post)." in stead of "Iidesune!".
This is all for today's post.
If you have any question, please don't hesitate to ask in a comment.
In the next post, I will write on how to ask question.
Have a good day!