Which dictionary are you using? Because your questions tell me that your dictionary is not giving you the concepts of the words properly. I recommend a better and easier to understand dictionary. I recommend the dictionary I wrote. Your questions are intelligent and well founded, you are working hard to learn, continue the good work.

As Alexandre said, they all "affirm" in one way or another. I could just give the dictionary definitions, but If I were to hear them in every day speech, though, the main differences I see are: Certify: this is when someone wtih authority affirms something. For example, a driver's license is a type of certification given to those who earn it. Vertify (I think you mean Verify here): When something is "verified," it is examined in some way to make sure that it meets an expectation. For example, if you "verify" your message, you are confirming that it is accurate. Justify: To justify something is to try to defend it, or prove it to be correct. For example: I told someone a lie, but I tried to "justify" it by saying that I did not want to hurt their feelings with the truth. Testify: This is usually referring to the act of giving a hopefully truthful statement to a judge and/or jury during some kind of trial. It could also mean giving a statement with extreme passion/knowledge of what you are talking about. For example: The witness was called to the courtroom to "testify" and gave his statement to the judge. Warn: To warn someone is to try to let them know of something before it happens, usually to prevent some kind of danger to them, or to let them know something that they might not be aware of. For example: My friend "warned" me not to touch the stove because it was recently used and still hot. Alarm: This is similar to warn, in that it is usually to let people know of something dangerous or unexpected. However, alarm is not always before something happens--it can also be used during or after the event. This can also be associated with devices such as a "fire alarm", which will make a loud noise to alert people of a fire. Alert: Again, this is similar to warn and alarm. However, being "alert" means that you are already aware of something. It can also mean being vigilant, or being fully conscious and aware. For example, The town was on alert after they heard about the storm headed their way. Another example: After drinking many cups of coffee, I was fully alert at 3a.m. Hope this helps :)

All of them takes you to affirm something :p