Think of it as having a 'username' and 'password'. With the 'username' (wallet address), people can send money to you. However, you need the password (private key) to be able to send coins out.
If you have the address, you can't figure out the private key except through brute force, but with the private key you can easily solve to get the address.
Thanks for the quick reply
Could you please give me more technical reply .... I'm giving you an idea of what I know and what I don't
what do I know / don't know is given below, within "===="
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I have has used public , private keys in e-mail and I understand the following i.e.
= When I get into this business I have a key pair
= Recipient (in the mail world) has a key pair
= I encrypt to the recipient's *public* key
= So everyone publishes his own public key
= keyservers hold public keys
= web of trust / some form of authentication is used to connect a real face to a public key
= I can sign plain text with my public key , but signing only provides authenticity IF my public key is authentic and used by me ...but noting more
What sort of user am I : I use a computer that is connected to the internet ...well how on earth would I other wise find you nice guys / girls
I do NOT understand
= how to generate the next biggest prime #
= how exactly the encryption process works (i.e.) what is Hash, which hash is strongest etc
I do NOT understand
= anything about linux
= how to create a bootable linux
= which linux is good / bad etc
I can remember passphrases
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with this level of knowledge what / where can I read to understand a wallet ..., the block chain, what is a transaction and so on