any help with building a deck for magic the gathering?

Try a Red-Black-White deck. If you can structure it so that the Black and White cards don't annihilate your own deck, you end up with a deck that swarms the opponent while giving you bonuses and abilities from the moment you draw the card until the moment it is removed from the game, and I don't mean just sent to the Graveyard, either. For example.

White has powerful creatures, such as Clerics, Soldiers, and Angels. When placed on the field, they become staunch allies. And when they wind up in the Graveyard, use spells like Raise Dead and Overcrowded Cemetery to return key players to your hand or even straight to the field, and in the meantime boosting the power of certain black creatures. Meanwhile, Red harasses the enemy for cheap while you build a sufficient Manna Pool to power Blacks' spells and Whites' creatures.

OK, so the first thing you do is add lands that produce those colors of mana, mountains for red, swamps for black, and forests for green. It should total to about 24 cards now. Next, add creatures that share a color with the lands you produce. Remember to have the low-casting cards relatively more than the high-casting ones. Next, add instants, sorceries, enchantments, artifacts, planeswalkers, just to get in a good mix. They should match the theme of your deck. The recommended number of cards is 60, but you can exceed that number, but remember: the less cards you have, the more likely you will draw what you need.

try think of the cards that will help ur cards the most for each individual color. also try to keep the land count to a moderate amount u dont want to be mana flooded. also if ur wanting to run all the three colors try looking up jund cards on magicthegathering gatherer. if ur focusing on one theme for each try keeping red for speed,black for creature hate,green for mana ramp. good luck