PTSD is short for Post Traumatic Stress Disorder. 
Simply put, a life threatening event or repeated trauma that causes unpleasant memories at a later time when triggered by stress.
See PTSD resources below.

For those that serve or who have served, unpleasant events can be heightened by their experiences during military service. The feelings from an unpleasant event is different for everybody and can arise from a wide range of situations before, during, or after military service.
These scary memories interfere with their normal day and may make them feel uneasy or unsafe leading to trouble sleeping or avoiding others or situations that remind them of the trauma. They may develop anxiety, depression, insomnia, and isolation. 
See PTSD resources below.

Suicide is when people harm themselves with the intent of ending their life, and they die as a result. A suicide attempt is when people harm themselves with the intent of ending their life, but they do not die.

Suicide is not a normal response to stress. Suicidal thoughts or actions are a sign of extreme distress and should not be ignored. If these warning signs apply to you or someone you know, get help as soon as possible, particularly if the behavior is new or has increased recently. 
See Suicide Awareness resources below.

Be aware the warning signs of suicide: depression, anxiety, low self-esteem, hopelessness, or change in the way they act. 

Many Veterans don’t show any signs of an urge to harm themselves before doing so. But some may show signs like those of depression, anxiety, low self-esteem, or hopelessness:
-Seeming sad, depressed, anxious, or agitated most of the time
-Sleeping either all the time or not much at all
-Not caring about what they look like or what happens to them
-Pulling away from friends, family, and society
-Losing interest in hobbies, work, school, or other things they used to care about
-Expressing feelings of excessive guilt or shame, failure, lack of purpose in life, or being trapped

They may also change the way they act, and start to show signs like these:
-Perform poorly at work or school
-Act violently or take risks (like driving fast or running red lights)
-Do things to prepare for a suicide (like giving away special personal items, making a will, or seeking access to guns or pills).
[According to va.gov "Information for Family & Friends" website]

5 steps you can take to #BeThe1To help someone in emotional pain:    1. Ask.  2. Keep them Safe.  3. Be There.  4. Help them Connect.  5. Stay Connected. 
See Suicide Awareness resources below.