Your wallet holds money that isn't in a trading account. Your trading accounts are your MetaTrader 5 (MT5) accounts, where you trade.
Wallet balance: money in your wallet, available for deposits and transfers.
Total balance: your wallet plus your live trading accounts.
Pending in and Pending out: money on its way into or out of your wallet.
To trade with money in your wallet, move it to a trading account with Transfer under Manage Funds. See 'How do I move money between my wallet and my trading accounts?'