Lightning Component:

<!--SampleComponent.cmp--> 
<aura:component implements="flexipage:availableForAllPageTypes,force:appHostable" access="global">
    <!--Declare Attributes-->
    <aura:attribute name="vfMsgMethod" type="object" description="this attribute is for visualforce page javascript method"/>
    
    <!--Component Start--> 
    <div class="slds-m-around_xx-large">
        <lightning:button variant="Brand" class="slds-button" label="Submit" onclick="{!c.doAction}"/>
    </div>
    <!--Component End-->
</aura:component>

Lightning Controller:

({
    doAction : function(component, event, helper) {
        var msg = 'Welcome to Salesforce Ohana';
        var msgMethod = component.get("v.vfMsgMethod");
        msgMethod(msg, function(){
            //handle callback
        });
    }
})

Lightning App:

<!--SampleApp.app--> 
<aura:application extends="ltng:outApp" access="global">
    <!--Lightning component-->
    <aura:dependency resource="c:SampleComponent"/>
</aura:application>

Visualforce Page:

<apex:page sidebar="false" showHeader="false">
    <apex:includeLightning />
    <!--Lightning Container-->
    <div style="width:100%;height:100px;" id="LightningContainer"/>
    
    <script type="text/javascript">
    //Create Lightning Component
    $Lightning.use("c:SampleApp", function() {
        $Lightning.createComponent("c:SampleComponent", { 
            vfMsgMethod : getMessage, //Method to call from lightning component
        },"LightningContainer", function(component) {
            console.log('Component created');
        });
    });
    
    //Function to call from Lightning Component
    function getMessage(welcomeMsg){
        alert(welcomeMsg);
    }
    </script>
</apex:page>

Output: