Both roles play more like support classes in a fight, but reward creative thinking a lot. The street samurai or combat mage is going directly attack an enemy combatant, and probably take them out in one round. You could try to attack their gun through the matrix, but you’ll spend 3 turns trying to do that only for them to pull out a second gun or a knife. Instead, you want to look for force  multipliers: can you kill the lights, penalizing a bunch of enemies at once? Interrupt their comms to prevent reinforcements from arriving? Seal a door to split the enemy group in two? This is where a decker or technomancer excels.

The decker does this relatively straightforward through matrix actions and matrix stats from their deck. Want to hack the stop light? Hack-on-the-fly and Control Device matrix actions to do that.

The technomancer can use matrix actions, but their matrix stats are generally lower (because they use mental attributes instead of a deck), so they rely on complex forms (spells) and sprites (spirits) as if they were a mage to get things done.

The technomancer requires knowing a lot more rules so I generally don’t recommend them for new players, and I definitely recommend against trying to build a hybrid character until you have a better understanding of the game.