Hi  Saurabh Bisht 19
-------------------------------------------------Html file ----------------------------------------------------------------------
<template>
      <div>
        <div class="slds-p-around_medium lgc-bg">
            <lightning-input type="text" label="first name" onchange={firstNames}></lightning-input>
        </div>
        <div class="slds-p-around_medium lgc-bg">
            <lightning-input type="text" label="lastname"  onchange={lastNames}></lightning-input>
        </div>
        <div class="slds-p-around_medium lgc-bg">
            <lightning-combobox
            name="progress"
            label="Account"
            value={value}
            placeholder="Select Progress"
            options={options}
            onchange={handleChange} ></lightning-combobox>
        </div>
        <lightning-button label="submit" onclick={createContact}> </lightning-button>
      </div>
</template>


 ----------------------------------------------------------------------------------------js File-------------------------------------------------------------------------------

import { LightningElement } from 'lwc';
import getallAccount from '@salesforce/apex/CreateContact.allAccount'
import createContact from '@salesforce/apex/CreateContact.createContact'
export default class Createcontact extends LightningElement {
    account = '';
    firstName = '';
    lastName = ''
    options = []
    constructor() {
        super();
        this.getAccountInfo();
    }
    getAccountInfo() {
        getallAccount().then(item => {
            this.options = item.map(items => {
                return {
                    label: items.Name,
                    value: items.Id
                }
            })
        })
    }
    handleChange(event) {
        this.account = event.detail.value;
    }
    firstNames(event) {
        this.firstName = event.detail.value;
        console.log(this.firstName);
    }
    lastNames(event) {
        this.lastName = event.detail.value;
        console.log(this.lastName);
    }

    createContact() {
        console.log(this.lastName, this.firstName, this.account);
        createContact({ "Fname": this.firstName, "Lname": this.lastName, "accountId": this.account }).then(item => {
            console.log("value insrted");
        })
    }
}
--------------------------------------------------- Apex Controller -----------------------------------------------------------------------
public  without sharing class CreateContact {
    @AuraEnabled(cacheable=false)
    public static list<Account> allAccount(){
            list<account> accountList =[SELECT Id,Name from Account]; 
            system.debug('accountList:::'+accountList);
           return accountList;
    }
      @AuraEnabled(cacheable=false)
    public static void createContact(string Fname, string Lname, string accountId){
        try{
              system.debug('Fname'+Fname);
            system.debug('Lname'+Lname);
            system.debug('Fname'+Fname);
            if(Fname != null && Lname != null && accountId != null){
                contact cont = new contact();
                cont.LastName =Lname;
                cont.AccountId = accountId;
                cont.FirstName =Fname;
                insert cont; 
            }
        
        }catch(Exception ex){
             system.debug('Exception::'+ex.getMessage()+'at'+ex.getLineNumber());
            
        }
    }
}

 if it is helpful for you please mark it as the best answer
 thank you