In 5E, there is no RAW that requires training in a given skill in order to attempt an action. You simply declare what you want to do, and the DM picks the DC. If you have proficiency in the skill, you get to add your proficiency bonus. Otherwise, it's just an ability check.
How do you determine strength in D&D?
An ability score is determined by rolling 4d6 and discard the lowest score. This is repeated six times and each score is placed next to the ability where they are wanted by the player. This method tends to produce higher than average scores, which is more appropriate for a heroic character.
How can I buy DND point?
Point buy is one of the 3 methods of determining ability scores that are described on page 13 of the Player's Handbook. Essentially point buy starts every PC out with an 8 in each of the 6 ability scores. From here you can increase each stat by using the 27 points that are given to each player.