Generate CSR with Private Key with following steps:

1. Log in to ACS and click System Configuration.
2. Click ACS Certificate Setup.
3. Click Generate Certificate Signing Request and fill out the Generate New Request form:

Required files are:
CN=yourdomain.com - domain name which will be secured,
O=Company - organization,
L=Cracow - town or city,
S=Mazowieckie  - state,
C=PL - two letters country code.

Optional file:
OU=IT - company unit

Note:
The following characters should not be used when typing in your CSR input: < > ~ ! @ # $ % ^ / \ ( ) ? , &

4. In the Private key file box enter the path where you would like to save your key, e.g. C:\privatekey.key.
5. Enter a private key password (file Private key password).
6. Choose Key length from the list (minimum is 2048-bit).
7. In the Digest to sign with select SHA1.
8. Click Submit button to approve typed data.
9. Your CSR file will be displayed on the right. Copy it to Notepad (with BEGIN and END CSR lines). You will need it to issue SSL certificate.