You delegate your NYM using the official NYM wallet. Make sure you buy native NYM which are currently only available on Kraken and not the ERC20 token!
Article: How to delegate your NYM to a mixnode
Step 1: Buy native NYM on Kraken
Step 2: Install the official Wallet (Mac, Windows, Linux)
Step 3: Send the NYM to your own wallet
Step 4: In the wallet choose "Delegate"
Step 5: Enter Mixnode Identity "38zcSsvjXsAX7C28ko2H3Lt55X4TYxfZYkPADxKXZHUj", amount to delegate and klick "Delegate stake"
Step 5: You can check the accumulated rewards by entering your wallet's address here
Enter your address in the search bar, hit enter and see you claimable rewards: