The short version: Sell it on an exchange that exchanges for fiat. Like with gdax and coinbase, you can simply link your PayPal (they accept PayPal withdrawals) and just sell your btc on gdax and withdraw the fiat to your coinbase account then withdraw to paypal.
Kraken and bitstamp and many other exchanges have fiat to bank account, which is less ideal, but also doable.
Other than that you can sell on here... just choose someone with a lot of green trust.
You can also safely sell on localbitcoins because they have an escrow system where you wont release the bitcoin until the funds have arrived.
to sell your bitcoin assets instantly, you can do it through local bitcoin sites in your country or also through other exchange sites as there are many exchange sites that can also swap BTC with USD. I currently use VIP exchange websites to sell my BTC assets and at a cost of 0.3% on the number of BTCs you will sell.
Yes there are countries which have sites or apps that could let bitcoin holders to convert directly to their national currency. In my country, mostly use this method to pay bills and send money.