'This' means αυτός, and 'man' means άντρας but think about it a bit more rationally.
This one. Who? The man.
Αυτός. Ποιος; Ο άντρας.
Αυτός is always accompanied by an article, if you're using it meaning this and not he.
Αυτός ο άντρας - This man.
Αυτό το τραπέζι - This table.
Αυτός είναι καλός - He is nice.
I hope it's understandable ^.^
I frequently make mistakes in word order with αυτός and its friends and relations. When do I say: "αυτός ο άντρας", "ο αυτός άντρας", or "ο άντρας αυτός". Are some of these wrong sometimes? Do they have different meanings? I normally get this right but I do not understand why?
Yes, it is. Αυτός άντρας would be grammatically incorrect.
Αυτός could mean both he and this (when you're refering to sth of masculine gender.)
When you use it as this, you need an article.
Αυτός ο άντρας - This man
Αυτό το κορίτσι - This girl
Αυτή η γυναίκα - This woman
When you use it as he, the article is of course unnecessary.
(Αυτός) είναι καλός - He is nice
(Αυτό) είναι δύσκολο - It is difficult
Αυτή είναι εδώ - She is here.
(Note how the pronouns in the first two examples are in parethesis. This is because each gender has it's own adjective ending. So, since there is an indication of the gender, the pronoun becomes unnecessary. However, in the third example, εδώ is an adverb, threfore theres no indication for the gender. The pronoun probably wouldn't be necessary in spoken Greek -since you would probably know the gender from the subject of your discussion-, but in written Greek, you may need the pronoun in order to be clear. This is of course, irrelevant to your question, but I thought it would be nice to mention it in order for you to not get surprised by sudden pronoun omissions later. ^.^)