You can make a fighter and choose to become an Eldritch Knight. You dont get the more powerful spells but you are able to use magic while wearing the heaviest of plate.
To be specific, you get to learn 2 cantrips and 4 Lv 1 spells, and get 3 Lv 1 slots that are restored on long rest. They don't need to prepare spells since their pool of known spells is rather limited to begin with (they are all automatically prepared) but they can only pick EK and start casting at Lv 3. By comparison, by Lv 4, a wizard knows 4 cantrips and 10 Lv 1-2 spells (in addition to any they learn from scrolls), of which they can prepare 7 and cast using 4 Lv 1 slots and 3 Lv 2 slots.
TLDR: EK can use spells to soften up high-AC enemies or enemies at range; but they aren't really a caster class.
