user21738: I simply want to store one small string in the blockchain. That's it. I am reading here a step by step guide but there is little in terms of explanation beyond the code snippets. What I would like to know is if essentially the problem is this...
There are two parties: me and someone else. I need to somehow get that "someone else's" address, and can figure out the rest from there.
But the main problem is, I don't have any "someone else" I would like to send the money to (or even need to send money to). I simply want to place something in the blockchain.
How are people doing this in their tutorials? Who are they sending the money to? Are they just creating a "dummy transaction" against a "dummy address" of some sort, and then getting a refund of the money? That way it seems the data would still be in the blockchain, but then no money would be spent (other than a potential processing tax fee).
If so, how do I do that? Am I supposed to setup two bitcoin networks, and send data from one to the other? That is, create a transaction of sending money from one to the other? Or perhaps even easier (though not possible?), I can get two addresses from my bitcoin node, and then send money from one of those addresses to another. Is that possible?

user100212: Nothing prevents you to send bitcoins to one of your own addresses. I guess I'd just create a new address on my node with bitcoin-cli getnewaddress, and then create a transaction with 2 outputs :

one to the address I just got with my whole input amount (minus mining fees)
another to a "dummy" address (can be one you generated with the same method, you can't spend it anyway!) with OP_RETURN + [your_data], and of course 0 as amount

As for the exact way to do this, the post you linked too seems like it could work, but I never tested it myself. The idea is to create the transaction first with the createrawtransaction method from bitcoin-cli, and then modify a piece of the data with yours.
As I said I never did that, I highly suggest you try it out on testnet first, there are many things that could just go wrong.

21738: <p>I simply want to store one small string in the blockchain. That's it. I am reading <a href="https://bitcoin.stackexchange.com/questions/25224/what-is-a-step-by-step-way-to-insert-data-in-op-return">here</a> a step by step guide but there is little in terms of explanation beyond the code snippets. What I would like to know is if essentially the problem is this...</p>

<p>There are two parties: me and someone else. I need to somehow get that "someone else's" address, and can figure out the rest from there.</p>

<p>But the main problem is, I don't have any "someone else" I would like to send the money to (or even need to send money to). I simply want to place something in the blockchain.</p>

<p>How are people doing this in their tutorials? Who are they sending the money to? Are they just creating a "dummy transaction" against a "dummy address" of some sort, and then getting a refund of the money? That way it seems the data would still be in the blockchain, but then no money would be spent (other than a potential processing tax fee).</p>

<p>If so, how do I do that? Am I supposed to setup two bitcoin networks, and send data from one to the other? That is, create a transaction of sending money from one to the other? Or perhaps even easier (though not possible?), I can get two addresses from my bitcoin node, and then send money from one of those addresses to another. Is that possible?</p>
 100212: <p>Nothing prevents you to send bitcoins to one of your own addresses. I guess I'd just create a new address on my node with <code>bitcoin-cli getnewaddress</code>, and then create a transaction with 2 outputs :</p>

<ul>
<li>one to the address I just got with my whole input amount (minus mining fees)</li>
<li>another to a "dummy" address (can be one you generated with the same method, you can't spend it anyway!) with OP_RETURN + [your_data], and of course 0 as amount</li>
</ul>

<p>As for the exact way to do this, the post you linked too seems like it could work, but I never tested it myself. The idea is to create the transaction first with the <code>createrawtransaction</code> method from bitcoin-cli, and then modify a piece of the data with yours.</p>

<p>As I said I never did that, I highly suggest you try it out on testnet first, there are many things that could just go wrong.</p>
