You need to set home domain for your issuer account and host valid https://<domain>/.well-known/stellar.toml file on your domain with image=<logo url>. And don't forget about CORS headers, otherwise browser won't be able to access your stellar.toml file
According to documentation here:
Here's simple example:
desc="1 BTC token entitles you to receive 1 Bitcoin (minus outgoing transaction fee) to an address of your choice using our anchor."
conditions="Outgoing transaction fee deducted from the amount sent"