trader broker dealer...and some other terms difference, between, outside, current, example

John10

I have difficulties understanding the difference between a broker a dealer and a trader.

broker trades on behalf of the trader.
but what is the difference between a dealer and a trader?

moreover there is a low-cost-whatever-the-liquidity trading strategy:
The TRADER places a limit order outside the current bid-ask quotes in order to minimize trading costs. For example a trader may place a LIMIT BUY ORDER at a price below the current market bid. the sstrengt of this strategy is that commissions, spreads, and market impact costs tend to be low....

i dont't understand this - if somebody (here the trader) wants to buy securites - doesn't he have to place an order the ask rate.

I think my general confusion is from which perspective to we see this? if i want to buy securites, i look at the ask price - the dealer quotes the bid ( the price at which he buyssecurities) and the ask(price at which he sells securites).

so if i want to place a limit buy order. do i see this from perspective of investor or trader???

thanks.