How do I know 360 Security antivirus app really works?

I have an Alcatel one touch fiercexl & 360 Security is the antivirus/cleaner app I have. I'm not entirely sure it even works like it says it should. Aft I use it & leave the app, and then go right back to it, it seems like (almost always) it'll have just as much (if not the same) things to do. Like Clearing cache, cool down battery, boost, etc. Also if I get a message that says"warning your alcatel has viruses, & You have to do an antivirus scan before phone is damaged" it always says phone is secure no viruses detected. Then why did I get the message in the first place? Is it also fixing the problem while scanning? Also why doesn't cleaning junk also cover app cache? It makes you do it manually in advanced clear. How do I know if it is actually working correctly or if I need a different antivirus? Can you recommend one for me if I need it?