The plugin registers a Twig variable:

craft.superFavourite

{% set isSaved = craft.superFavourite.isFavourited(entry.id) %}

{% if isSaved %}
    Saved
{% else %}
    Not saved yet
{% endif %}

Pass a collection ID to check a specific collection:

{% set isSaved = craft.superFavourite.isFavourited(entry.id, collection.id) %}

{% set ids = craft.superFavourite.getFavouritedElementIds() %}

Filter by collection:

{% set ids = craft.superFavourite.getFavouritedElementIds(collection.id) %}

Filter by element type:

{% set ids = craft.superFavourite.getFavouritedElementIds(null, 'craft\\elements\\Entry') %}

Use IDs in a Craft element query:

{% set savedEntries = craft.entries()
    .id(ids)
    .all() %}

getCollections() returns global collections and collections owned by the current user.

{% set collections = craft.superFavourite.getCollections() %}

{% for collection in collections %}
    <h2>{{ collection.name }}</h2>
    <p>{{ collection.description }}</p>
{% endfor %}

{% set globalCollections = craft.superFavourite.collections()
    .userId(null)
    .all() %}

{% set personalCollections = currentUser
    ? craft.superFavourite.collections().userId(currentUser.id).all()
    : [] %}

{% set collection = craft.superFavourite.collections()
    .handle('wishlist')
    .one() %}

{% set favourites = craft.superFavourite.favourites()
    .collectionId(collection.id)
    .all() %}

{% set favourites = craft.superFavourite.favourites()
    .collectionId(collection.id)
    .all() %}

{% for favourite in favourites %}
    {% set elementQuery = craft.superFavourite.createElementQuery(favourite.elementType) %}
    {% set element = elementQuery ? elementQuery.id(favourite.elementId).one() : null %}

    {% if element %}
        <article>
            <h2>{{ element.title ?? 'Untitled' }}</h2>
            {% if element.url %}
                <a href="{{ element.url }}">View</a>
            {% endif %}
        </article>
    {% endif %}
{% endfor %}

{% set wishlist = craft.superFavourite.getCollectionByHandle('wishlist') %}

This method uses the current user. For global-only lookups, use the collection query:

{% set globalWishlist = craft.superFavourite.collections()
    .userId(null)
    .handle('wishlist')
    .one() %}

Current user's favourite count:

{{ craft.superFavourite.getFavouriteCount() }}

Current user's count in one collection:

{{ craft.superFavourite.getFavouriteCount(collection.id) }}

Collection item count from the element:

{{ collection.getItemCount() }}

Direct query count:

{{ craft.superFavourite.favourites()
    .collectionId(collection.id)
    .count() }}

{% set elementTypes = craft.superFavourite.getAvailableElementTypes() %}

{% for type in elementTypes %}
    <option value="{{ type.value }}">{{ type.label }}</option>
{% endfor %}