Sure no problem.
For epic affix. There's 2 ways to roll epic (orange) affix via crystal,1) angelite or 2) topaz.
Because Topaz is a rare crystal you may not have any yet. Instead you can use angelite which are plentiful. Apply angelite to your gear. If you don't have an empty affix space you can use kyanite to remove an affix (gear can have 6 affixes). Apply angelite. If you get a normal (yellow) affix you can remove with kyanite & try again. Once you get an epic affix, you can reroll with sapphire until you get the affix you want.
This won't matter yet, but in the future you may want to use emerald crystal to upgrade the quality of your gear to 25% max. Also use Peridot to max the gear level to 100. You need 100 level, 25% quality gear to roll perfect affixes which will be important later in the game.
To craft a mythic affix, you need a gear with 4 empty slots. Gear can drop with 4 empty slots or you can use Zircon to make a slot. Then use this reference to add mythstones to the gear.