Use "help sendtoaddress" command on the console (or with bitcoin-cli)... it explains fairly well how to use it with a couple of examples:
sendtoaddress "address" amount ( "comment" "comment_to" subtractfeefromamount replaceable conf_target "estimate_mode" )
Send an amount to a given address.
Requires wallet passphrase to be set with walletpassphrase call.
Arguments:
1. address (string, required) The bitcoin address to send to.
2. amount (numeric or string, required) The amount in BTC to send. eg 0.1
3. comment (string, optional) A comment used to store what the transaction is for.
This is not part of the transaction, just kept in your wallet.
4. comment_to (string, optional) A comment to store the name of the person or organization
to which you're sending the transaction. This is not part of the
transaction, just kept in your wallet.
5. subtractfeefromamount (boolean, optional, default=false) The fee will be deducted from the amount being sent.
The recipient will receive less bitcoins than you enter in the amount field.
6. replaceable (boolean, optional, default=fallback to wallet's default) Allow this transaction to be replaced by a transaction with higher fees via BIP 125
7. conf_target (numeric, optional, default=fallback to wallet's default) Confirmation target (in blocks)
8. estimate_mode (string, optional, default=UNSET) The fee estimate mode, must be one of:
"UNSET"
"ECONOMICAL"
"CONSERVATIVE"
Result:
"txid" (string) The transaction id.
Examples:
> bitcoin-cli sendtoaddress "1M72Sfpbz1BPpXFHz9m3CdqATR44Jvaydd" 0.1
> bitcoin-cli sendtoaddress "1M72Sfpbz1BPpXFHz9m3CdqATR44Jvaydd" 0.1 "donation" "seans outpost"
> bitcoin-cli sendtoaddress "1M72Sfpbz1BPpXFHz9m3CdqATR44Jvaydd" 0.1 "" "" true
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "sendtoaddress", "params": ["1M72Sfpbz1BPpXFHz9m3CdqATR44Jvaydd", 0.1, "donation", "seans outpost"] }' -H 'content-type: text/plain;'
http://127.0.0.1:8332/NOTE: this won't allow you to specify specific inputs to use (or addresses to spend FROM)... if you want to do that and can't use the GUI to specify the inputs you want to spend, you'll need to do something like "createrawtransaction"...