When you're near an anvil, you can merge 2 items held in both hands together to receive a new one.

You have an array of weapons and upgrades accessible exclusively to Artificers. Check your Artifice Logs tab in your advancements for the recipes. (There are 5 weapons & 2 upgrades available right now)
The weapons and all ingredients are listed below.

Flamethrower (iron block + gunpowder x2 + redstone dust): projects a piercing ray of fire that burns enemies.
Blast Shield (iron ingot + gold ingot + shield): explodes if damaged while holding the shield, however the shield will go on a cooldown shortly after being deployed.
Snapfreeze (iron block x2 + gunpowder + snow block): fires a freezing gust of ice that stuns the first entity hit. If it's below 30% HP, it will die upon taking damage.
Spore Blaster: (iron block + gunpowder + warped fungus): fires a spore cloud that either boosts enemies' attack damage and reduces armor OR reduces attack damage but increases speed.
Eclipse Shield (shield + nether star): dashes when you stop blocking with the shield, making your next attack apply Darkness. If the attack hits an enemy with Darkness, it sets them on fire.

Petricite Chip: makes Cybernetic Heart (see below) heal you for 1 HP whenever you take magic damage.
Nanotech Update Chip: makes Cybernetic Heart give extra +8 Armor & +6 Armor Toughness.
Geothermal Chip: makes you be able to restore hunger via eating Blaze Powder & Lava Buckets.

Your heart is fueled by nanomachines. You don't need to eat (nor can you eat) and natural regeneration doesn't work for you, but you rapidly restore health when standing still, draining hunger to do so. Hunger restores slowly over time.
The higher your hunger bar is, the faster you'll regenerate.

The weight of your augments together with heavy armor would ruin your body, so you can't wear armor better than iron.