There's no safest way to purchase bitcoin, it's either you purchase bitcoin from a centralised exchange (cex) or Decentralised exchange (Dex). Both of the exchanges are Safe for someone to purchase bitcoin. It all depends on individual preferences. But I will suggest you use centralised exchange, it will be easier for you to understand. As a newbie that haven't purchased bitcoin for the first time,  you might find Dex a bit challenging to understand.