how to install android untivirus and instert an external SD card for storage purposes My android has been hit by a virus and I can't recover my space even if I delete some files it still says I have 0 B and when I insert an 8 GB memory card its not reading what should I do
Ok first, antivirus in the classical sense is almost useless on android. Due to the strong security sandboxing, antivirus apps can only detect malicious apps based on signatures but cannot stop or remove them. So you need to take care yourself to get rid of the malware. 

Second, viruses in the classical sense also rarely exist on android, so please provide more infos on what exactly your malware is doing. If I got you right, you have some problem with blocked/filled up storage. 

Third, just to exclude something completely independent of malware activity, did you ever use the newly inserted sd card in an android phone?  You may need to format the card before it can be used, see storage settings. 

Summary: please check if your sd card is properly formatted and also provide more details on your problem and the malware you assume you have on your phone.