It sounds like you haven't quite figured out how the RPG's battle system works. When you see enemies on the map while you're running around, you can choose to avoid them, try to sneak up on them or just plow right into them. Or in some cases, they catch up to you before you're out of range. However it happens, once you contact an enemy the battle begins. Once you're in battle you cannot switch your equipment around, you just fight until you kill the enemies or you're killed (in which case no big loss since you can just retry the battle).
My advice is not to worry about which weapons to use before each and every battle. Just equip the strongest you've got and use general accessories like the HP+ bangles until you're comfortable with the way the equipment/battle systems work. 90% of the time you will not need specialized equipment for any given battle, especially in the early stages of the game.
The game does offer tutorials about how battle works, did you skip those? If you did you might consider going back and actually letting the game walk you through those first few encounters, it will really help you learn how it all works. I didn't skip them and it still took me half the game to really get a handle on everything. If you're lost now it'll be even worse later when the combat system starts gaining depth and tactics become very important to winning.
~DragonHeart~
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