This is a summary of the main Jinja2 Blocks syntax that can be used with Ansible playbook for daily basis operations and maintenance:

Print variable or Expression

Print the variable by using the variable name surrounded by double braces.

{‌{ my_var }}
# .i.e: {‌{ ansible_distribution }}

Filters

Variables can be transformed/modified by filters.

Think about filter as a function

{‌{ my_var | my_filter }}
# .i.e : {‌{ app_title | capitalize }}

Read it like my_filter(my_var)

If Block

{% if CONDITION1 %}
    blah blah blah
{% elif CONDITION2 %}
    blahelif blahelif blahelif .
{% else %}
    blahelse so far
{% endif %}

#.i.e

{% if git_branch == 'master' %}
     RELEASE: {‌{ app_version }}
{% else %}
    SNAPSHOT: {‌{ app_version }}-RC{‌{ build_number }} 
{% endif %}

For Loop

{% for ELEMENT in ARRAY %}
   Process {‌{ ELEMENT }}
{% endfor %}

#. i.e: assume that ( app_pages = ["login.html", "index.html"] )

{% for page in app_pages %}
   <a href="https://example.com/{‌{ page }}">{‌{ page }}</a>
{% endfor %}