The neutral game is a state where both players have no advantage, both have equal footing and advantages & disadvantages have not appeared yet. Once someone gets a signifcant hit or has limited their opponents options (whether it be shielding,dodging or attacking) advantages start to appear, meaning that person won the neutral game. The neutral game can be one by applying what is called pressure, which is essentially poking their shield while stage safe in order to create openings. Always remember this attacking beats grabs, grabs be shielding, and shielding beats attacking.

Edgeguarding

Edgeguarding happens once your opponent gets knocked of stage. You can chase them off stage, limiting their recovery options or reading where they're going to recover in order to get damage or possibly the stock.

Reads

Reading is a psychological strategy where you observe your opponents habits in order to punish them. Reads can take all of sorts of shapes and sizes and its a completely pshychological idea. You can condition your opponent by letting them use certain attacks and only punishing it when you know you can take their stock. There is no right or wrong way to read, it's all up to you.