you get that by being helpful and active, if ppl like your reply they can give you rep or you can hold a giveaway that tends to get users the fastest rep but ofc thats all up to you.
if you look in the bottom right corner of this reply you can see the grey and while heart, click it and pick an emote. That is how you give others +rep and others can do that to your reply/posts aswell, just remember any attempt of fake rep farming will result in a perma ban so dont try and farm with ya friends