onrowselection can be used to handle selectedRows in lightning:dataTable.The keyField should be mapped to a unique identifier attribute from the payload.

Sample Code:

Component:

<aura:component implements="force:appHostable"
       controller="AccountListController">
                
    <aura:attribute type="Account[]" name="acctList"/>
    <aura:attribute name="mycolumns" type="List"/>
    <aura:attribute name="selectedAccts" type="List"/>
    
    <aura:handler name="init" value="{!this}" action="{!c.init}"/>
    
    <div class="slds-box slds-theme_default">
        
        <lightning:datatable data="{! v.acctList }" 
                             columns="{! v.mycolumns }" 
                             keyField="Id"
                             onrowselection="{!c.handleSelect}"/>
        <br/>
        <center>
            <lightning:button onclick="{!c.showSelectedName}" label="Show" variant="brand"/>
        </center>
        
    </div>
    
</aura:component>

Controller:

({
    
    init : function(component, event, helper) {
        
        component.set('v.mycolumns', [
            {label: 'Account Name', fieldName: 'linkName', type: 'url', 
            typeAttributes: {label: { fieldName: 'Name' }, target: '_blank'}},
            {label: 'Industry', fieldName: 'Industry', type: 'text'},
            {label: 'Type', fieldName: 'Type', type: 'Text'}
        ]);
        
        helper.fetchAccounts(component, event);
        
    },
    
    handleSelect : function(component, event, helper) {
        
        var selectedRows = event.getParam('selectedRows'); 
        var setRows = [];
        for ( var i = 0; i < selectedRows.length; i++ ) {
            
            setRows.push(selectedRows[i]);

        }
        component.set("v.selectedAccts", setRows);
        
    },
    
    showSelectedName : function(component, event, helper) {
        
        var records = component.get("v.selectedAccts");
        for ( var i = 0; i < records.length; i++ ) {
         
            alert(records[i].Name);
            
        }
    }

})

Helper:

({
    
 fetchAccounts : function(component, event) {
  
        var action = component.get("c.fetchAccts");
        
        action.setCallback(this, function(response) {
            
            var state = response.getState();
            
            if (state === "SUCCESS") {
                
                var records = response.getReturnValue();
                records.forEach(function(record) {
                    
                    record.linkName = '/' + record.Id;
                    record.CheckBool = false;
                    
                });   
                
                component.set("v.acctList", records);
                
            }            
            
        });
        
        $A.enqueueAction(action);
        
 }
    
})

Apex Class:

public class AccountListController {
    
    @AuraEnabled
    public static List < Account > fetchAccts() {
        
        return [ SELECT Id, Name, Industry, Type FROM Account LIMIT 5 ];
        
    }
    
}

Output: