You can discard this card and any other Machine-type monster to summon it. In other words, since it can be summoned through the first effect; use it as part of the cost along with any other Machine-type monster.
A good way to Special Summon this card on the first turn is to Normal Summon "Scrap Recycler" and send this card to the Graveyard. Then discard two Level 4 machines to Special Summon it, and then use the effect of "Recycler" to return the two Level 4 Machines to your deck and draw 1 card.
You only have to discard 8 or more Levels' worth of Machine-Type monsters from your hand in order to Special Summon this card.
Summon any of the "Gadget" monsters, then add another "Gadget" to your hand, then discard the new "Gadget" and "Machina Fortress" to special summon "Machina Fortress", to summon two monsters from your hand while losing nothing more from your hand.
You can use "Shreddder" to send "Machina Fortress" to the Graveyard and destroy one face-up monster your opponent controls (Level 7 or lower). Then you can discard more Machines to special summon "Machina Fortress".
This card works well with "Rope of Life" and by using it to suicide, you can destroy any card your opponent controls, then you can use "Rope of Life" during the Battle Phase and bring out a 3300 ATK Fortress and attack again (albeit with somewhat hefty cost).
You can also use "Miracle's Wake" or "Time Machine" instead to keep your hand, but the trade-off is that its ATK will remain at 2500.
Use "Pot of Avarice" to recover monsters you discarded for this card effect, while also getting 2 extra cards.
You can use this in a deck with "Malefic Cyber End Dragon" as it is a level 10 monster that can be used to pay the whole cost of this card's summon.
Vylon decks can also utilize this card as a back-up plan, simply by discarding this card along with any Vylon Tuners (except "Vylon Prism" and "Vylon Stella"), or simply discard 2 Vylon Union monsters.
You can also ram this card into a more powerful monster to destroy it with the battle effect, and since this card can be easily revived, it's no real loss unless this card is removed from play as a result of an opponent's card effect or by banishing it to summon Machina Gearframe.
You can use "Card of Safe Return" to draw 1 card every time this card is Special Summoned from the Graveyard.
All Machine-Type monsters that can be discarded on their own to Special Summon "Machina Fortress" are as follows: