Definition of earlier
When a player plays "earlier", he is in earlier position, in other words, he is among the first to play preflop. The most "earlier" position is Under The Gun (UTG). He is first to speak preflop. Depending on the number of players at the table, there may be UTG+1 and UTG+2 next. These three positions generally form the so-called "earlier" positions. Then come the players in "middle position" (MP1 and MP2) or "hijack" and "lowjack" depending on the vocabulary you use. So, if we recapitulate, the positions earlier, then middle, the cutoff, the button and the blinds.
What is the implication of playing in earlier?
When playing in earlier (EP), we have to take into account several aspects. First, we talk first without knowing what the other players have done. We have no clues about the strength of their hand. We have to be careful with these positions. If a hand like matching J7 can open very well from the knob, such a hand in UTG position or in earlier position in general will be almost impossible to pay off. In earlier, you'll want to be more conservative, especially if you're a beginner. If you can play more than 50% of your hands profitably from the button, it is not a mistake to play as little as hijack% of your UTG hands. On the other hand, when bluffing, if you are earlier, you will be given a lot of credit.