To start adding plugins and editing your server via the panel, you first need to sign in! (If you don't have a Minehut account, just create one!) After you have signed in / created your account, you need to link your Minecraft player with your account. To do this, go to your Minehut page, and navigate to the top right, click the down arrow that's right next to your profile, and click account settings. Once in Account Settings, the top-left section (there should be 3, next to a tab that says "Credit Tansactions") should have a "link account" button. Click that and follow the instructions to link your account! After you've linked your account, refresh Minehut, and you should have access to your server! (Sorry if this was a bit much lol)
Let me know if you need further help!