best way to lvl up your hime/heroes is either doin ultimate event (which can be very difficult if you are new), or doing daily dungeon on Sundays, its called Gold Cave and it rewards alot of exp and money but almost no drops. It also gives alot of ranking points which will alow you to rank up faster and thus gain more Soul P that you need to unlock new hero souls.
As for weapons, you have 2 options here: either constantly run raid of the element you want, since they drop SR-tier weapons of corresponding element. Not often, but they do drop. Otherwise, and in my opinion better way, is to participate in events: event shop sells one SSR-tier weapon (right now its a lance) and 3 different SR-tier weapons of the event element (fnow its fire) As a new player you might not be able to do Ultimate or expert difficulty, but even standard should be enough to get you at least one copy of SSR weapon, which in turn will make you able to clear expert difficulty on next event, which in turn will allow you to get better weapon, and clear higher difficulty, etc, etc.
Of course, if you dont mind spending some $$$ on gambling, you can always do some gacha which might end you up with great himes/weapons... or leave you heartbroken...