Usually a trust beneficiary will start by asking the trustee to make a distribution. And that's a wise thing to do. If you can solve the problem by simply having a conversation then by all means do it.
Unfortunately, some trustees will not respond to reasonable conversations or reasonable requests. Some trustees won't even respond to a letter. Some trustees won't respond no matter what you do. If that's your situation it is time to get a trust litigation attorney involved.
There are a number of reasons a trustee will decline to make a distribution. Probably the most common reason is the trustee doesn't understand the trust. The trustee had some conversation or thinks they remember some conversation that they had some time ago with the person who created the trust. Their memory of that conversation is different from what the trust itself actually says. The trustee does the wrong thing and relies on their memory rather than the terms of the trust.
Sometimes a trustee doesn't make the distribution because they're just plain lazy. Even though they've got a duty to act and the duty to administer the trust according to its terms they still don't make distributions even when the trust calls for those distributions.
Some trustees won't make distributions because they've done something wrong and they're hoping to cover it up by not making the distribution. The trustee may have mismanaged trust assets or, in some cases, wrongfully taken trust assets for themselves. If you've also made a request for information about the trust (for example, what assets were in the trust when the settlor died, how trust money has been spent, what assets are left in the trust, etcetera) and the trustee will not give you the information and will not make a distribution to you then this may well be your situation.
If you're going to get your distribution then you are probably going to need to file a petition with the probate court. The petition may be as straightforward as asking the probate court to compel a distribution. It's possible the petition will also include a request to make the trustee account and, if necessary, to surcharge the trustee for any losses the beneficiaries have suffered due to the trustee. If the trustee is believed to have taken trust property too then the petition will demand the trustee return the property and, in some cases, pay double damages.
If you've taken reasonable steps to get your distribution and the trustee won't give it to you then do something about it NOW. Bad situations that are allowed to fester often get worse with time. You can't afford to allow somebody who is incompetent or dishonest to remain in control of your inheritance.