In order to hold a balance of a specific asset, you first need to add a trustline for that asset in your wallet. Adding a trustline is the equivalent of telling the Stellar network that you trust that asset and it is ok for other wallets to send you that asset.
Your wallet MUST be funded with XLM in order to add a trustline. If you do not have any XLM in your wallet, you will not be able to add trust. To fund your wallet with some XLM, you can receive a XLM payment or deposit some non-XLM asset
To add a trustline using Stellarport:
- Navigate to your Wallet page
- Go to the Balances page
- Click "+ Trustline" (NOTE: this button will only appear if you have a non-zero XLM balance)
- Choose the asset you would like to hold and add trust to (and then click Finished)