What is the best all-around lens for a Sony mirrorless camera if I can only afford one? I just bought a used a6400 and it came with this tiny flat lens but everyone says it isnt very good and I honestly have no idea where to even start looking for a better one. I'm going to Tokyo in about three months and I really want to take nice pictures of the shrines and the street food but I dont want to be that person constantly switching glass pieces every five minutes plus my bag is already gonna be pretty full. My budget is probably around $600 max because the camera itself already cost me a lot of my savings.

I keep seeing things like 24-70mm or 18-135mm and the numbers are just making my head spin because I dont know what they actually mean in real life. Like do I need a big number or a small number for taking a picture of a bowl of ramen?? I'm mostly looking for:

• something that can zoom in and out
• something that works when it's kind of dark out
• not too heavy to carry all day

Sorry if this is a super basic question but the more I read on blogs the more confused I get with all the technical talk about apertures and crop factors and stuff. I just want one lens that stays on the camera and works for everything and I'm totally lost...