Why do we need to keep some BNB on the wallet balance even if operate with BUSD smart-contracts?
First of all we will describe BNB purposes and what is it in general:
BNB is a native coin (like TRX in Tron, and ETH in Ethereum networks) in Binance Ecosystem that provides variety of usage cases:
Pay for trading fees on the Binance exchange;
Pay for trading fees on Binance DEX (Decentralized Exchange);
Pay for transaction fees on the Binance Smart Chain;
Provide liquidity on Binance Liquid Swap;
For other less popular but still useful actions.
Let's take in our focus Binance Smart Chain network. First of all it was created for decentralized apps and smart-contracts development. On the basis of this network there were created multiple different tokens - virtual currency token or a denomination of a cryptocurrency. It represents a tradable asset or utility that resides on blockchain.
In Binance Smart Chain network all tokens have their own standard - BEP20 (for example ETH uses ERC20, TRX - TRC20 standards).
Binance USD (BUSD) is a 1:1 USD-backed stable coin issued by Binance (in partnership with Paxos). It is approved and regulated by the New York State Department of Financial Services (NYDFS).
Its tokens are present in different blockchain networks so as in Binance Smart Chain and uses BEP20 standard here.
Let's get back to BNB coin and its importance for any action in BSC network.
As we mentioned above BNB used to supply all fees in BSC. So when you want to send, for example, BUSD from one address to another, or to interact with smart-contract you need to have some amount of BNB on your address balance to cover BSC network fees. Here is screenshot with random transaction details in BSC network:
Important: If your BNB balance on address is zero then you won't be able to start any transaction of any token in BSC network. If we mentioning FORSAGE registration or further levels activation - you won't be able to do this either without BNB amount on your balance.
BNB and BUSD - are they located in one place in the wallet?
Yes, when you created BSC address in any supported app you can just add BUSD BEP20 token to the list. This way you will see all balances without any further actions. Here is an example how it looks like in Token Pocket app:
What is the way to fund your balances and be prepared for transactions?
The easiest way to manage and keep both balances above zero is to purchase BNB BEP20 first. After you see it on your wallet balance, add BUSD BEP20 token to the list (if you haven't done it yet) and use token swap/exchange in your wallet application. Make sure you kept some BNB for network fees.
What is the way to track all transactions and income to/from your BSC wallet address?
Just like TRX and ETH, Binance Smart Chain uses it's own Explorers for this purposes.
One of the main is BscScan
There you can paste and see any address details: all transactions, all time related requests, all fees consumption and real time gas fee rates.
Few words about security.
Treat your cryptocurrency assets like your physical ones. Never share your security keys from wallet addresses with anyone, don't keep the keys in common mail boxes, files, or phones. Remember if you lost your recovery keys, no matter how much assets are in there - you won't be able to access to it anymore. So be cautious!