x509 Certificate Signature I've got a question about the signature of a CA.

As I understand, the CA takes the public key of the client and signs it with
his own private key by using "md5WithRSAEncryption" (like explained here: http://en.wikipedia.org/wiki/X.509#Sample_X.509_certificates".
What does it mean exactly?
Can you give me a formal explanation for better understanding?
Does the CA use both algorithms?

Second question
In the first certificate example from wikipedia in section 'Subject Public Key Info:' there is defined the 'RSA Public Key:'
Is that the plain public key which the CA got from the Client or is there something done on it?

Please give more hints for better understanding if you can.

Thanks before
Signing with "md5WithRSAEncryption" means CA calculates MD5 hash to get an integer first and apply his private RSA key next to produce the signature. A DER-encoded string is the input to the hash. Client (Subject in X.509 parlance) data, including public key, is described with ASN.1 language, "to be signed" part of specification. Certificate extensions (v3) are also included into "to be signed".

"Plain" public key, as received from client, is encoded according to X.509 specifications. See ASN.1 description at PKCS 10, "certificate request".

Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile
Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile