To use the API add this as a file in your project:

using System;
using UnityEngine;

public interface IGizmosAPI
{
        public Material GetDefaultMaterial();
        public void SetDefaultMaterialPass(int pass = 0);
        public void DrawWithReference(Transform reference, Action drawMethod);
        public void  DrawOnGlobalReference(Action drawMethod);
        public void DrawWithOrthoProjection(Action drawMethod);
        public void DrawAxis(float headSize, Color color, Vector3 offset);
        public void DrawTransform(Transform transform, float headSize, Color color);
        public void DrawCollider(Collider collider, Color color);
        public void DrawShape(Shape shape, Color color);

        public void DrawSimpleWireframeCube(Vector3 offset, Color color);
        public void DrawWireframeCube(Vector3 foward, Vector3 up, Vector3 right, Vector3 offset, Color color);
        public void DrawWireframeCircle(float radius, Vector3 normal, Vector3 up, Vector3 offset, Color color, int resolution = 3, float startAngle = 0f, float endAngle = 2f * Mathf.PI, bool isWholeCircle = true);
        public void DrawSimpleWireframeSphere(float radius, Vector3 offset, Color color, int resolution);
        public void DrawWireframeSphere(float radius, Vector3 offset, Vector3 foward, Vector3 up, Color color, int resolution = 3);
        public void DrawWireframeHemisphere(float radius, Vector3 offset, Vector3 foward, Vector3 up, Color color, int resolution = 3);
        public void DrawWireframeCapsule(float radius, Vector3 startPoint, Vector3 endPoint, Color color, int resolution = 3);
        public void DrawSimpleWireframeCapsule(float radius, float height, Vector3 up, Vector3 offset, Color color, int resolution = 3);
        public void DrawWireframeCone(float coneRadiusStart, float coneRadiusEnd, Vector3 coneStart, Vector3 coneEnd, Color color, int resolution = 3);
        public void DrawVector(Vector3 vector, float headSize, Vector3 offset, Color color);
}

And do ModHelper.Interaction.TryGetModApi<IGizmosAPI>("Locochoco.GizmosLibrary"); to be able to access the api calls.

See the examples to learn how to use each call from the API.