First off, learn level 10 firewall, and learn how to do vertical firewalls. That'll help you level. You might want to invest in a Phen card or Sweet Nightmare card once you get the zeny. That will prevent monsters from interrupting your spells. The best place to start leveling is to do the Eden Equipment quests. Free gear you can use up into third class, and it helps introduce areas where you can level.
A good starting point on making zeny, depending on your level, is to go to the map 1 east of Payon. You can hunt strawberries from the Spores there. There's usually a buy shop in Payon, or you can vend them. Eventually, buying and selling Kafra shop (cash shop) items will almost be a must if you want to buy very expensive endgame gear.
Making a merchant to buy pots and to sell stuff is an absolute must.
The shopping boards are a pain. You have to know the exact name of the item you want to look up, and each word MUST be capitalized. So if you want to look up scale shell, you would put "Scale Shell". If you don't know the full name of the item, you could put "Scale" and click on the Search Partial box. That will give you all of the results for anything that has "Scale" in the name.
And yes, if you place an item into the Kafra storage, all of the characters on that RO account can share that storage and access those items.
If you need any more help, check out irowiki.org or ask here. Good luck!