Trust is a gut instinct developed after observing a pattern of honesty and integrity over a period of time. You can't (force) yourself to trust someone nor can you force yourself to (believe) something that does not ring true for you. Even if you choose to "ignore" your instincts it will haunt you later on when the truth is revealed.
As for how one shows another they trust them it's not about handing over your car keys, house keys, lending money, or not asking questions. It's not a "calculated" decision to act but rather doing what comes (natural) to you in the moment.
So much of trust is really about people trusting themselves to (choose) trustworthy people as friends, lovers, or a spouse. Whenever someone says, "I don't trust anyone." What they are really saying is "I don't trust (myself) to choose wisely."