How can I make the tooo long articles short and just show a excerpt or snippet from it with a link to the total article
Try reading the blogger help page How can I create expandable post summaries? Basically it requires some template modifications to do some css trickery. Seems like a hack, but then again I don't know how other blog software/services work, so I can't compare.
Depends on your blogging software. If you are talking about WordPress (based on the blog in your profile) then you want to click the "More" button where you want the break to occur. Or type <!--more--> HTML: where you want the break to be in your post