The following applies to summoning spells:
They do not have a target.
They do not have to be within the Wizard's forward arc.
The Wizard does not need line of sight.
Summoning spells always target a point on the battlefield unless specified. The summoned unit or terrain must be wholly within the spell's range. If a summoned unit, models or terrain feature cannot be placed because there is not enough room, they do not enter play at all, though the spell's lore attribute may still apply. If you do not have appropriate models for the summoning spell, then that spell cannot be cast.
Summoning Terrain
Summoned terrain features can be placed within 1" of or on top of other units, simply place the units in or on the terrain feature without changing their facing or formation.
Summoning Units
When placing a summoned unit, it must be wholly at least 1" away from impassable terrain and other units. It can be placed facing any direction and in any legal formation. Unless specified, this unit does not have any upgrades or command models, and the unit does not count as having moved this turn. Summoned units do not award victory points under any circumstances.
Summoning Models
Some augment spells can summon models into already existing units. This is done in a strict order. First, any slain command groups models are resurrected in an order of your choosing, displacing rank-and-file models as required. Then rank-and-file models with multiple Wounds are healed to their starting value. Lastly, rank and file models are summoned. The unit formation must be legal after all models are added. If any models cannot be added for any reason, those models are wasted. Any models that are summoned into an existing unit retain any equipment, rules and/or bonuses as the rest of the unit.