If you want to generate signing certificate for your android app with OpenSSL, you can use library in this way:
Create a key:
$ openssl genrsa -out android_distribution.key 2048
Generate a request:
$ openssl req -new -key android_distribution.key -out android_distribution.csr
Self-signing:
$ openssl x509 -req -days 10950 -in android_distribution.csr \ > -signkey android_distribution.key -out android_distribution.crt
Transform .crt в .p12:
$ openssl pkcs12 -export -in android_distribution.crt \ > -inkey android_distribution.key -out android_distribution.p12
Don't forget to store your data somewhere safe.
UPDATE:
If you need keystore for example for phonegap build you can canvert your certificate:
$ keytool -importkeystore -srckeystore android_distribution.p12 \ > -srcstoretype PKCS12 -destkeystore android_distribution.jks -deststoretype JKS
The end.