Don't be intimidated by other people with powerful teams, the honest truth is this game requires time. The longer you play the more your team will grow and the more stuff you can do.
Gods are obtained through the rare egg machine (REM) and you have to spend 5 magic stones to have a chance at the machine. You can earn stones in game, and they are given away often.
Now onto specific advice, Haku is a wonderful starting lead and you should work on two things:
So step 1:
Make what is known as a 'resolve' team, making use of the leader skill of Ogres. The leader skill, resolve, lets you survive any single attack when your HP is above 70%.
[ Ice Ogre ] [ Blue Goblin ] [ Marine Goblin ] [ Marine Goblin ] [ Marine Goblin ]
You want the levels of these monsters to be as low as possible, so your HP is very very low. This lets you heal up faster, which works well with another common leader skill: Autoheal.
You would make the team above, and find friends who run one of the following leads or any of their evolutions with auto heal leader skills:
[ Enchantress of the Sea, Siren ] [ Mystical Forest Pixie, Alraune ] [ Messenger of God, Archangel ] [ Amaterasu Ohkami ]
These auto-heal leads, paired with a low HP team, and a leader with the "resolve" skill. Lets you survive high hitting attacks with ease, and this works well for the Friday weekly dungeon (25 stamina).
Now step 2:
Early on your haku lacks subs if you get unlucky, but the dub-lits have wonderful stats at a low cost. They are great for new players to stack their teams early.
You want a team that looks something like this:
[ Incarnation of Byakko, Haku ] [ Dub-mythlit ] [ Dub-mythlit ] [ Dub-rubylit ] [ Dub-sapphilit ]
This team will help you progress pretty far into the normal dungons. You should focus on leveling up other potential subs for your team.
This thread on PadForums has a lot of good information on Haku teams.
Once you have a decent foundation, you should farm the Tower of Giants > Dragons of the Tower over and over again on weekends to rank up. During the week you can do whatever you like, but on weekends this dungeon is half of its normal stamina cost. This means until around 100 (or higher, I dont remember exactly) you can constantly run this dungeon without stopping, since you will level up before you run out of stamina.