Need help with gravity simulation in 2D game engine

I’m writing a 2D game engine using C++ and SDL2 and started implementing a rigidbody component similar to that of unity to my gameobjects. I have a method in the rigidbody class called AddForce which takes a 2D vector force as a parameter and calculates the velocity vector using F = M*A, I use this function to move the character left and right using the keyboard arrows. Now my question is, how do I manage the gravity with this and how do I calculate the resultant force of the gravity and the force applied when pressing either keyboard arrows. Here is the rigidbody class.

#ifndef RIGIDBODY_H #define RIGIDBODY_H  //Game engine libraries #include "gameEngine/Game.h" #include "gameEngine/GameObject.h" #include "gameEngine/Component.h" #include "gameEngine/components/Transform.h"  //GlM library #include "glm/glm.hpp"  class RigidBody : public Component { private:     Transform* m_transfrom; private:     float m_mass;     float m_acceleration;     glm::vec2 m_forceApplied;     glm::vec2 m_velocity; private:     float m_deltaTime;  public:     RigidBody(float mass)     {         m_name = "RigidBody";         m_mass = mass;         m_acceleration = 0;         m_forceApplied = glm::vec2(0,0);         m_velocity = glm::vec2(0,0);      } public:      void AddForce(glm::vec2 force, float deltaTime)      {            float forceMagnitude;         m_deltaTime = deltaTime;         m_forceApplied = force;          forceMagnitude = glm::length(force);         m_acceleration = forceMagnitude / m_mass;       }      private:      glm::vec2 CalculateVelocity()      {          float velocityMagnitude;          static glm::vec2 newVelocity = glm::vec2(0,0);           velocityMagnitude = m_acceleration * m_deltaTime;           if(m_forceApplied.x != 0 || m_forceApplied.y != 0)              newVelocity = glm::normalize(m_forceApplied);          else            newVelocity = glm::vec2(0,0);           newVelocity = newVelocity * velocityMagnitude;           return newVelocity;       }   public:     void Initialize() override     {         m_transfrom = m_owner->GetComponent<Transform>("Transform");     }     void Update(Game instance, float deltaTime) override     {         m_velocity += CalculateVelocity();         m_transfrom->position.x += m_velocity.x * deltaTime;         m_transfrom->position.y += m_velocity.y * deltaTime;     }     void Render() override     {      }  };   #endif